/*
 * hugetlbpage-backed filesystem.  Based on ramfs.
 *
 * Nadia Yvette Chambers, 2002
 *
 * Copyright (C) 2002 Linus Torvalds.
 * License: GPL
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/thread_info.h>
#include <asm/current.h>
#include <linux/sched/signal.h>         /* remove ASAP */
#include <linux/falloc.h>
#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/file.h>
#include <linux/kernel.h>
#include <linux/writeback.h>
#include <linux/pagemap.h>
#include <linux/highmem.h>
#include <linux/init.h>
#include <linux/string.h>
#include <linux/capability.h>
#include <linux/ctype.h>
#include <linux/backing-dev.h>
#include <linux/hugetlb.h>
#include <linux/pagevec.h>
#include <linux/parser.h>
#include <linux/mman.h>
#include <linux/slab.h>
#include <linux/dnotify.h>
#include <linux/statfs.h>
#include <linux/security.h>
#include <linux/magic.h>
#include <linux/migrate.h>
#include <linux/uio.h>

#include <linux/uaccess.h>

static const struct super_operations hugetlbfs_ops;
static const struct address_space_operations hugetlbfs_aops;
const struct file_operations hugetlbfs_file_operations;
static const struct inode_operations hugetlbfs_dir_inode_operations;
static const struct inode_operations hugetlbfs_inode_operations;

struct hugetlbfs_config {
        struct hstate           *hstate;
        long                    max_hpages;
        long                    nr_inodes;
        long                    min_hpages;
        kuid_t                  uid;
        kgid_t                  gid;
        umode_t                 mode;
};

int sysctl_hugetlb_shm_group;

enum {
        Opt_size, Opt_nr_inodes,
        Opt_mode, Opt_uid, Opt_gid,
        Opt_pagesize, Opt_min_size,
        Opt_err,
};

static const match_table_t tokens = {
        {Opt_size,      "size=%s"},
        {Opt_nr_inodes, "nr_inodes=%s"},
        {Opt_mode,      "mode=%o"},
        {Opt_uid,       "uid=%u"},
        {Opt_gid,       "gid=%u"},
        {Opt_pagesize,  "pagesize=%s"},
        {Opt_min_size,  "min_size=%s"},
        {Opt_err,       NULL},
};

#ifdef CONFIG_NUMA
static inline void hugetlb_set_vma_policy(struct vm_area_struct *vma,
                                        struct inode *inode, pgoff_t index)
{
        vma->vm_policy = mpol_shared_policy_lookup(&HUGETLBFS_I(inode)->policy,
                                                        index);
}

static inline void hugetlb_drop_vma_policy(struct vm_area_struct *vma)
{
        mpol_cond_put(vma->vm_policy);
}
#else
static inline void hugetlb_set_vma_policy(struct vm_area_struct *vma,
                                        struct inode *inode, pgoff_t index)
{
}

static inline void hugetlb_drop_vma_policy(struct vm_area_struct *vma)
{
}
#endif

static void huge_pagevec_release(struct pagevec *pvec)
{
        int i;

        for (i = 0; i < pagevec_count(pvec); ++i)
                put_page(pvec->pages[i]);

        pagevec_reinit(pvec);
}

/*
 * Mask used when checking the page offset value passed in via system
 * calls.  This value will be converted to a loff_t which is signed.
 * Therefore, we want to check the upper PAGE_SHIFT + 1 bits of the
 * value.  The extra bit (- 1 in the shift value) is to take the sign
 * bit into account.
 */
#define PGOFF_LOFFT_MAX \
        (((1UL << (PAGE_SHIFT + 1)) - 1) <<  (BITS_PER_LONG - (PAGE_SHIFT + 1)))

static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma)
{
        struct inode *inode = file_inode(file);
        loff_t len, vma_len;
        int ret;
        struct hstate *h = hstate_file(file);

        /*
         * vma address alignment (but not the pgoff alignment) has
         * already been checked by prepare_hugepage_range.  If you add
         * any error returns here, do so after setting VM_HUGETLB, so
         * is_vm_hugetlb_page tests below unmap_region go the right
         * way when do_mmap_pgoff unwinds (may be important on powerpc
         * and ia64).
         */
        vma->vm_flags |= VM_HUGETLB | VM_DONTEXPAND;
        vma->vm_ops = &hugetlb_vm_ops;

        /*
         * page based offset in vm_pgoff could be sufficiently large to
         * overflow a loff_t when converted to byte offset.  This can
         * only happen on architectures where sizeof(loff_t) ==
         * sizeof(unsigned long).  So, only check in those instances.
         */
        if (sizeof(unsigned long) == sizeof(loff_t)) {
                if (vma->vm_pgoff & PGOFF_LOFFT_MAX)
                        return -EINVAL;
        }

        /* must be huge page aligned */
        if (vma->vm_pgoff & (~huge_page_mask(h) >> PAGE_SHIFT))
                return -EINVAL;

        vma_len = (loff_t)(vma->vm_end - vma->vm_start);
        len = vma_len + ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
        /* check for overflow */
        if (len < vma_len)
                return -EINVAL;

        inode_lock(inode);
        file_accessed(file);

        ret = -ENOMEM;
        if (hugetlb_reserve_pages(inode,
                                vma->vm_pgoff >> huge_page_order(h),
                                len >> huge_page_shift(h), vma,
                                vma->vm_flags))
                goto out;

        ret = 0;
        if (vma->vm_flags & VM_WRITE && inode->i_size < len)
                i_size_write(inode, len);
out:
        inode_unlock(inode);

        return ret;
}

/*
 * Called under down_write(mmap_sem).
 */

#ifndef HAVE_ARCH_HUGETLB_UNMAPPED_AREA
static unsigned long
hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
                unsigned long len, unsigned long pgoff, unsigned long flags)
{
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma;
        struct hstate *h = hstate_file(file);
        struct vm_unmapped_area_info info;

        if (len & ~huge_page_mask(h))
                return -EINVAL;
        if (len > TASK_SIZE)
                return -ENOMEM;

        if (flags & MAP_FIXED) {
                if (prepare_hugepage_range(file, addr, len))
                        return -EINVAL;
                return addr;
        }

        if (addr) {
                addr = ALIGN(addr, huge_page_size(h));
                vma = find_vma(mm, addr);
                if (TASK_SIZE - len >= addr &&
                    (!vma || addr + len <= vm_start_gap(vma)))
                        return addr;
        }

        info.flags = 0;
        info.length = len;
        info.low_limit = TASK_UNMAPPED_BASE;
        info.high_limit = TASK_SIZE;
        info.align_mask = PAGE_MASK & ~huge_page_mask(h);
        info.align_offset = 0;
        return vm_unmapped_area(&info);
}
#endif

static size_t
hugetlbfs_read_actor(struct page *page, unsigned long offset,
                        struct iov_iter *to, unsigned long size)
{
        size_t copied = 0;
        int i, chunksize;

        /* Find which 4k chunk and offset with in that chunk */
        i = offset >> PAGE_SHIFT;
        offset = offset & ~PAGE_MASK;

        while (size) {
                size_t n;
                chunksize = PAGE_SIZE;
                if (offset)
                        chunksize -= offset;
                if (chunksize > size)
                        chunksize = size;
                n = copy_page_to_iter(&page[i], offset, chunksize, to);
                copied += n;
                if (n != chunksize)
                        return copied;
                offset = 0;
                size -= chunksize;
                i++;
        }
        return copied;
}

/*
 * Support for read() - Find the page attached to f_mapping and copy out the
 * data. Its *very* similar to do_generic_mapping_read(), we can't use that
 * since it has PAGE_SIZE assumptions.
 */
static ssize_t hugetlbfs_read_iter(struct kiocb *iocb, struct iov_iter *to)
{
        struct file *file = iocb->ki_filp;
        struct hstate *h = hstate_file(file);
        struct address_space *mapping = file->f_mapping;
        struct inode *inode = mapping->host;
        unsigned long index = iocb->ki_pos >> huge_page_shift(h);
        unsigned long offset = iocb->ki_pos & ~huge_page_mask(h);
        unsigned long end_index;
        loff_t isize;
        ssize_t retval = 0;

        while (iov_iter_count(to)) {
                struct page *page;
                size_t nr, copied;

                /* nr is the maximum number of bytes to copy from this page */
                nr = huge_page_size(h);
                isize = i_size_read(inode);
                if (!isize)
                        break;
                end_index = (isize - 1) >> huge_page_shift(h);
                if (index > end_index)
                        break;
                if (index == end_index) {
                        nr = ((isize - 1) & ~huge_page_mask(h)) + 1;
                        if (nr <= offset)
                                break;
                }
                nr = nr - offset;

                /* Find the page */
                page = find_lock_page(mapping, index);
                if (unlikely(page == NULL)) {
                        /*
                         * We have a HOLE, zero out the user-buffer for the
                         * length of the hole or request.
                         */
                        copied = iov_iter_zero(nr, to);
                } else {
                        unlock_page(page);

                        /*
                         * We have the page, copy it to user space buffer.
                         */
                        copied = hugetlbfs_read_actor(page, offset, to, nr);
                        put_page(page);
                }
                offset += copied;
                retval += copied;
                if (copied != nr && iov_iter_count(to)) {
                        if (!retval)
                                retval = -EFAULT;
                        break;
                }
                index += offset >> huge_page_shift(h);
                offset &= ~huge_page_mask(h);
        }
        iocb->ki_pos = ((loff_t)index << huge_page_shift(h)) + offset;
        return retval;
}

static int hugetlbfs_write_begin(struct file *file,
                        struct address_space *mapping,
                        loff_t pos, unsigned len, unsigned flags,
                        struct page **pagep, void **fsdata)
{
        return -EINVAL;
}

static int hugetlbfs_write_end(struct file *file, struct address_space *mapping,
                        loff_t pos, unsigned len, unsigned copied,
                        struct page *page, void *fsdata)
{
        BUG();
        return -EINVAL;
}

static void remove_huge_page(struct page *page)
{
        ClearPageDirty(page);
        ClearPageUptodate(page);
        delete_from_page_cache(page);
}

static void
hugetlb_vmdelete_list(struct rb_root_cached *root, pgoff_t start, pgoff_t end)
{
        struct vm_area_struct *vma;

        /*
         * end == 0 indicates that the entire range after
         * start should be unmapped.
         */
        vma_interval_tree_foreach(vma, root, start, end ? end : ULONG_MAX) {
                unsigned long v_offset;
                unsigned long v_end;

                /*
                 * Can the expression below overflow on 32-bit arches?
                 * No, because the interval tree returns us only those vmas
                 * which overlap the truncated area starting at pgoff,
                 * and no vma on a 32-bit arch can span beyond the 4GB.
                 */
                if (vma->vm_pgoff < start)
                        v_offset = (start - vma->vm_pgoff) << PAGE_SHIFT;
                else
                        v_offset = 0;

                if (!end)
                        v_end = vma->vm_end;
                else {
                        v_end = ((end - vma->vm_pgoff) << PAGE_SHIFT)
                                                        + vma->vm_start;
                        if (v_end > vma->vm_end)
                                v_end = vma->vm_end;
                }

                unmap_hugepage_range(vma, vma->vm_start + v_offset, v_end,
                                                                        NULL);
        }
}

/*
 * remove_inode_hugepages handles two distinct cases: truncation and hole
 * punch.  There are subtle differences in operation for each case.
 *
 * truncation is indicated by end of range being LLONG_MAX
 *      In this case, we first scan the range and release found pages.
 *      After releasing pages, hugetlb_unreserve_pages cleans up region/reserv
 *      maps and global counts.  Page faults can not race with truncation
 *      in this routine.  hugetlb_no_page() prevents page faults in the
 *      truncated range.  It checks i_size before allocation, and again after
 *      with the page table lock for the page held.  The same lock must be
 *      acquired to unmap a page.
 * hole punch is indicated if end is not LLONG_MAX
 *      In the hole punch case we scan the range and release found pages.
 *      Only when releasing a page is the associated region/reserv map
 *      deleted.  The region/reserv map for ranges without associated
 *      pages are not modified.  Page faults can race with hole punch.
 *      This is indicated if we find a mapped page.
 * Note: If the passed end of range value is beyond the end of file, but
 * not LLONG_MAX this routine still performs a hole punch operation.
 */
static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
                                   loff_t lend)
{
        struct hstate *h = hstate_inode(inode);
        struct address_space *mapping = &inode->i_data;
        const pgoff_t start = lstart >> huge_page_shift(h);
        const pgoff_t end = lend >> huge_page_shift(h);
        struct vm_area_struct pseudo_vma;
        struct pagevec pvec;
        pgoff_t next, index;
        int i, freed = 0;
        bool truncate_op = (lend == LLONG_MAX);

        memset(&pseudo_vma, 0, sizeof(struct vm_area_struct));
        vma_init(&pseudo_vma, current->mm);
        pseudo_vma.vm_flags = (VM_HUGETLB | VM_MAYSHARE | VM_SHARED);
        pagevec_init(&pvec);
        next = start;
        while (next < end) {
                /*
                 * When no more pages are found, we are done.
                 */
                if (!pagevec_lookup_range(&pvec, mapping, &next, end - 1))
                        break;

                for (i = 0; i < pagevec_count(&pvec); ++i) {
                        struct page *page = pvec.pages[i];
                        u32 hash;

                        index = page->index;
                        hash = hugetlb_fault_mutex_hash(h, current->mm,
                                                        &pseudo_vma,
                                                        mapping, index, 0);
                        mutex_lock(&hugetlb_fault_mutex_table[hash]);

                        /*
                         * If page is mapped, it was faulted in after being
                         * unmapped in caller.  Unmap (again) now after taking
                         * the fault mutex.  The mutex will prevent faults
                         * until we finish removing the page.
                         *
                         * This race can only happen in the hole punch case.
                         * Getting here in a truncate operation is a bug.
                         */
                        if (unlikely(page_mapped(page))) {
                                BUG_ON(truncate_op);

                                i_mmap_lock_write(mapping);
                                hugetlb_vmdelete_list(&mapping->i_mmap,
                                        index * pages_per_huge_page(h),
                                        (index + 1) * pages_per_huge_page(h));
                                i_mmap_unlock_write(mapping);
                        }

                        lock_page(page);
                        /*
                         * We must free the huge page and remove from page
                         * cache (remove_huge_page) BEFORE removing the
                         * region/reserve map (hugetlb_unreserve_pages).  In
                         * rare out of memory conditions, removal of the
                         * region/reserve map could fail. Correspondingly,
                         * the subpool and global reserve usage count can need
                         * to be adjusted.
                         */
                        VM_BUG_ON(PagePrivate(page));
                        remove_huge_page(page);
                        freed++;
                        if (!truncate_op) {
                                if (unlikely(hugetlb_unreserve_pages(inode,
                                                        index, index + 1, 1)))
                                        hugetlb_fix_reserve_counts(inode);
                        }

                        unlock_page(page);
                        mutex_unlock(&hugetlb_fault_mutex_table[hash]);
                }
                huge_pagevec_release(&pvec);
                cond_resched();
        }

        if (truncate_op)
                (void)hugetlb_unreserve_pages(inode, start, LONG_MAX, freed);
}

static void hugetlbfs_evict_inode(struct inode *inode)
{
        struct resv_map *resv_map;

        remove_inode_hugepages(inode, 0, LLONG_MAX);
        resv_map = (struct resv_map *)inode->i_mapping->private_data;
        /* root inode doesn't have the resv_map, so we should check it */
        if (resv_map)
                resv_map_release(&resv_map->refs);
        clear_inode(inode);
}

static int hugetlb_vmtruncate(struct inode *inode, loff_t offset)
{
        pgoff_t pgoff;
        struct address_space *mapping = inode->i_mapping;
        struct hstate *h = hstate_inode(inode);

        BUG_ON(offset & ~huge_page_mask(h));
        pgoff = offset >> PAGE_SHIFT;

        i_size_write(inode, offset);
        i_mmap_lock_write(mapping);
        if (!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root))
                hugetlb_vmdelete_list(&mapping->i_mmap, pgoff, 0);
        i_mmap_unlock_write(mapping);
        remove_inode_hugepages(inode, offset, LLONG_MAX);
        return 0;
}

static long hugetlbfs_punch_hole(struct inode *inode, loff_t offset, loff_t len)
{
        struct hstate *h = hstate_inode(inode);
        loff_t hpage_size = huge_page_size(h);
        loff_t hole_start, hole_end;

        /*
         * For hole punch round up the beginning offset of the hole and
         * round down the end.
         */
        hole_start = round_up(offset, hpage_size);
        hole_end = round_down(offset + len, hpage_size);

        if (hole_end > hole_start) {
                struct address_space *mapping = inode->i_mapping;
                struct hugetlbfs_inode_info *info = HUGETLBFS_I(inode);

                inode_lock(inode);

                /* protected by i_mutex */
                if (info->seals & F_SEAL_WRITE) {
                        inode_unlock(inode);
                        return -EPERM;
                }

                i_mmap_lock_write(mapping);
                if (!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root))
                        hugetlb_vmdelete_list(&mapping->i_mmap,
                                                hole_start >> PAGE_SHIFT,
                                                hole_end  >> PAGE_SHIFT);
                i_mmap_unlock_write(mapping);
                remove_inode_hugepages(inode, hole_start, hole_end);
                inode_unlock(inode);
        }

        return 0;
}

static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
                                loff_t len)
{
        struct inode *inode = file_inode(file);
        struct hugetlbfs_inode_info *info = HUGETLBFS_I(inode);
        struct address_space *mapping = inode->i_mapping;
        struct hstate *h = hstate_inode(inode);
        struct vm_area_struct pseudo_vma;
        struct mm_struct *mm = current->mm;
        loff_t hpage_size = huge_page_size(h);
        unsigned long hpage_shift = huge_page_shift(h);
        pgoff_t start, index, end;
        int error;
        u32 hash;

        if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
                return -EOPNOTSUPP;

        if (mode & FALLOC_FL_PUNCH_HOLE)
                return hugetlbfs_punch_hole(inode, offset, len);

        /*
         * Default preallocate case.
         * For this range, start is rounded down and end is rounded up
         * as well as being converted to page offsets.
         */
        start = offset >> hpage_shift;
        end = (offset + len + hpage_size - 1) >> hpage_shift;

        inode_lock(inode);

        /* We need to check rlimit even when FALLOC_FL_KEEP_SIZE */
        error = inode_newsize_ok(inode, offset + len);
        if (error)
                goto out;

        if ((info->seals & F_SEAL_GROW) && offset + len > inode->i_size) {
                error = -EPERM;
                goto out;
        }

        /*
         * Initialize a pseudo vma as this is required by the huge page
         * allocation routines.  If NUMA is configured, use page index
         * as input to create an allocation policy.
         */
        memset(&pseudo_vma, 0, sizeof(struct vm_area_struct));
        vma_init(&pseudo_vma, mm);
        pseudo_vma.vm_flags = (VM_HUGETLB | VM_MAYSHARE | VM_SHARED);
        pseudo_vma.vm_file = file;

        for (index = start; index < end; index++) {
                /*
                 * This is supposed to be the vaddr where the page is being
                 * faulted in, but we have no vaddr here.
                 */
                struct page *page;
                unsigned long addr;
                int avoid_reserve = 0;

                cond_resched();

                /*
                 * fallocate(2) manpage permits EINTR; we may have been
                 * interrupted because we are using up too much memory.
                 */
                if (signal_pending(current)) {
                        error = -EINTR;
                        break;
                }

                /* Set numa allocation policy based on index */
                hugetlb_set_vma_policy(&pseudo_vma, inode, index);

                /* addr is the offset within the file (zero based) */
                addr = index * hpage_size;

                /* mutex taken here, fault path and hole punch */
                hash = hugetlb_fault_mutex_hash(h, mm, &pseudo_vma, mapping,
                                                index, addr);
                mutex_lock(&hugetlb_fault_mutex_table[hash]);

                /* See if already present in mapping to avoid alloc/free */
                page = find_get_page(mapping, index);
                if (page) {
                        put_page(page);
                        mutex_unlock(&hugetlb_fault_mutex_table[hash]);
                        hugetlb_drop_vma_policy(&pseudo_vma);
                        continue;
                }

                /* Allocate page and add to page cache */
                page = alloc_huge_page(&pseudo_vma, addr, avoid_reserve);
                hugetlb_drop_vma_policy(&pseudo_vma);
                if (IS_ERR(page)) {
                        mutex_unlock(&hugetlb_fault_mutex_table[hash]);
                        error = PTR_ERR(page);
                        goto out;
                }
                clear_huge_page(page, addr, pages_per_huge_page(h));
                __SetPageUptodate(page);
                error = huge_add_to_page_cache(page, mapping, index);
                if (unlikely(error)) {
                        put_page(page);
                        mutex_unlock(&hugetlb_fault_mutex_table[hash]);
                        goto out;
                }

                mutex_unlock(&hugetlb_fault_mutex_table[hash]);

                /*
                 * unlock_page because locked by add_to_page_cache()
                 * page_put due to reference from alloc_huge_page()
                 */
                unlock_page(page);
                put_page(page);
        }

        if (!(mode & FALLOC_FL_KEEP_SIZE) && offset + len > inode->i_size)
                i_size_write(inode, offset + len);
        inode->i_ctime = current_time(inode);
out:
        inode_unlock(inode);
        return error;
}

static int hugetlbfs_setattr(struct dentry *dentry, struct iattr *attr)
{
        struct inode *inode = d_inode(dentry);
        struct hstate *h = hstate_inode(inode);
        int error;
        unsigned int ia_valid = attr->ia_valid;
        struct hugetlbfs_inode_info *info = HUGETLBFS_I(inode);

        BUG_ON(!inode);

        error = setattr_prepare(dentry, attr);
        if (error)
                return error;

        if (ia_valid & ATTR_SIZE) {
                loff_t oldsize = inode->i_size;
                loff_t newsize = attr->ia_size;

                if (newsize & ~huge_page_mask(h))
                        return -EINVAL;
                /* protected by i_mutex */
                if ((newsize < oldsize && (info->seals & F_SEAL_SHRINK)) ||
                    (newsize > oldsize && (info->seals & F_SEAL_GROW)))
                        return -EPERM;
                error = hugetlb_vmtruncate(inode, newsize);
                if (error)
                        return error;
        }

        setattr_copy(inode, attr);
        mark_inode_dirty(inode);
        return 0;
}

static struct inode *hugetlbfs_get_root(struct super_block *sb,
                                        struct hugetlbfs_config *config)
{
        struct inode *inode;

        inode = new_inode(sb);
        if (inode) {
                inode->i_ino = get_next_ino();
                inode->i_mode = S_IFDIR | config->mode;
                inode->i_uid = config->uid;
                inode->i_gid = config->gid;
                inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
                inode->i_op = &hugetlbfs_dir_inode_operations;
                inode->i_fop = &simple_dir_operations;
                /* directory inodes start off with i_nlink == 2 (for "." entry) */
                inc_nlink(inode);
                lockdep_annotate_inode_mutex_key(inode);
        }
        return inode;
}

/*
 * Hugetlbfs is not reclaimable; therefore its i_mmap_rwsem will never
 * be taken from reclaim -- unlike regular filesystems. This needs an
 * annotation because huge_pmd_share() does an allocation under hugetlb's
 * i_mmap_rwsem.
 */
static struct lock_class_key hugetlbfs_i_mmap_rwsem_key;

static struct inode *hugetlbfs_get_inode(struct super_block *sb,
                                        struct inode *dir,
                                        umode_t mode, dev_t dev)
{
        struct inode *inode;
        struct resv_map *resv_map;

        resv_map = resv_map_alloc();
        if (!resv_map)
                return NULL;

        inode = new_inode(sb);
        if (inode) {
                struct hugetlbfs_inode_info *info = HUGETLBFS_I(inode);

                inode->i_ino = get_next_ino();
                inode_init_owner(inode, dir, mode);
                lockdep_set_class(&inode->i_mapping->i_mmap_rwsem,
                                &hugetlbfs_i_mmap_rwsem_key);
                inode->i_mapping->a_ops = &hugetlbfs_aops;
                inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
                inode->i_mapping->private_data = resv_map;
                info->seals = F_SEAL_SEAL;
                switch (mode & S_IFMT) {
                default:
                        init_special_inode(inode, mode, dev);
                        break;
                case S_IFREG:
                        inode->i_op = &hugetlbfs_inode_operations;
                        inode->i_fop = &hugetlbfs_file_operations;
                        break;
                case S_IFDIR:
                        inode->i_op = &hugetlbfs_dir_inode_operations;
                        inode->i_fop = &simple_dir_operations;

                        /* directory inodes start off with i_nlink == 2 (for "." entry) */
                        inc_nlink(inode);
                        break;
                case S_IFLNK:
                        inode->i_op = &page_symlink_inode_operations;
                        inode_nohighmem(inode);
                        break;
                }
                lockdep_annotate_inode_mutex_key(inode);
        } else
                kref_put(&resv_map->refs, resv_map_release);

        return inode;
}

/*
 * File creation. Allocate an inode, and we're done..
 */
static int hugetlbfs_mknod(struct inode *dir,
                        struct dentry *dentry, umode_t mode, dev_t dev)
{
        struct inode *inode;
        int error = -ENOSPC;

        inode = hugetlbfs_get_inode(dir->i_sb, dir, mode, dev);
        if (inode) {
                dir->i_ctime = dir->i_mtime = current_time(dir);
                d_instantiate(dentry, inode);
                dget(dentry);   /* Extra count - pin the dentry in core */
                error = 0;
        }
        return error;
}

static int hugetlbfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
{
        int retval = hugetlbfs_mknod(dir, dentry, mode | S_IFDIR, 0);
        if (!retval)
                inc_nlink(dir);
        return retval;
}

static int hugetlbfs_create(struct inode *dir, struct dentry *dentry, umode_t mode, bool excl)
{
        return hugetlbfs_mknod(dir, dentry, mode | S_IFREG, 0);
}

static int hugetlbfs_symlink(struct inode *dir,
                        struct dentry *dentry, const char *symname)
{
        struct inode *inode;
        int error = -ENOSPC;

        inode = hugetlbfs_get_inode(dir->i_sb, dir, S_IFLNK|S_IRWXUGO, 0);
        if (inode) {
                int l = strlen(symname)+1;
                error = page_symlink(inode, symname, l);
                if (!error) {
                        d_instantiate(dentry, inode);
                        dget(dentry);
                } else
                        iput(inode);
        }
        dir->i_ctime = dir->i_mtime = current_time(dir);

        return error;
}

/*
 * mark the head page dirty
 */
static int hugetlbfs_set_page_dirty(struct page *page)
{
        struct page *head = compound_head(page);

        SetPageDirty(head);
        return 0;
}

static int hugetlbfs_migrate_page(struct address_space *mapping,
                                struct page *newpage, struct page *page,
                                enum migrate_mode mode)
{
        int rc;

        rc = migrate_huge_page_move_mapping(mapping, newpage, page);
        if (rc != MIGRATEPAGE_SUCCESS)
                return rc;
        if (mode != MIGRATE_SYNC_NO_COPY)
                migrate_page_copy(newpage, page);
        else
                migrate_page_states(newpage, page);

        return MIGRATEPAGE_SUCCESS;
}

static int hugetlbfs_error_remove_page(struct address_space *mapping,
                                struct page *page)
{
        struct inode *inode = mapping->host;
        pgoff_t index = page->index;

        remove_huge_page(page);
        if (unlikely(hugetlb_unreserve_pages(inode, index, index + 1, 1)))
                hugetlb_fix_reserve_counts(inode);

        return 0;
}

/*
 * Display the mount options in /proc/mounts.
 */
static int hugetlbfs_show_options(struct seq_file *m, struct dentry *root)
{
        struct hugetlbfs_sb_info *sbinfo = HUGETLBFS_SB(root->d_sb);
        struct hugepage_subpool *spool = sbinfo->spool;
        unsigned long hpage_size = huge_page_size(sbinfo->hstate);
        unsigned hpage_shift = huge_page_shift(sbinfo->hstate);
        char mod;

        if (!uid_eq(sbinfo->uid, GLOBAL_ROOT_UID))
                seq_printf(m, ",uid=%u",
                           from_kuid_munged(&init_user_ns, sbinfo->uid));
        if (!gid_eq(sbinfo->gid, GLOBAL_ROOT_GID))
                seq_printf(m, ",gid=%u",
                           from_kgid_munged(&init_user_ns, sbinfo->gid));
        if (sbinfo->mode != 0755)
                seq_printf(m, ",mode=%o", sbinfo->mode);
        if (sbinfo->max_inodes != -1)
                seq_printf(m, ",nr_inodes=%lu", sbinfo->max_inodes);

        hpage_size /= 1024;
        mod = 'K';
        if (hpage_size >= 1024) {
                hpage_size /= 1024;
                mod = 'M';
        }
        seq_printf(m, ",pagesize=%lu%c", hpage_size, mod);
        if (spool) {
                if (spool->max_hpages != -1)
                        seq_printf(m, ",size=%llu",
                                   (unsigned long long)spool->max_hpages << hpage_shift);
                if (spool->min_hpages != -1)
                        seq_printf(m, ",min_size=%llu",
                                   (unsigned long long)spool->min_hpages << hpage_shift);
        }
        return 0;
}

static int hugetlbfs_statfs(struct dentry *dentry, struct kstatfs *buf)
{
        struct hugetlbfs_sb_info *sbinfo = HUGETLBFS_SB(dentry->d_sb);
        struct hstate *h = hstate_inode(d_inode(dentry));

        buf->f_type = HUGETLBFS_MAGIC;
        buf->f_bsize = huge_page_size(h);
        if (sbinfo) {
                spin_lock(&sbinfo->stat_lock);
                /* If no limits set, just report 0 for max/free/used
                 * blocks, like simple_statfs() */
                if (sbinfo->spool) {
                        long free_pages;

                        spin_lock(&sbinfo->spool->lock);
                        buf->f_blocks = sbinfo->spool->max_hpages;
                        free_pages = sbinfo->spool->max_hpages
                                - sbinfo->spool->used_hpages;
                        buf->f_bavail = buf->f_bfree = free_pages;
                        spin_unlock(&sbinfo->spool->lock);
                        buf->f_files = sbinfo->max_inodes;
                        buf->f_ffree = sbinfo->free_inodes;
                }
                spin_unlock(&sbinfo->stat_lock);
        }
        buf->f_namelen = NAME_MAX;
        return 0;
}

static void hugetlbfs_put_super(struct super_block *sb)
{
        struct hugetlbfs_sb_info *sbi = HUGETLBFS_SB(sb);

        if (sbi) {
                sb->s_fs_info = NULL;

                if (sbi->spool)
                        hugepage_put_subpool(sbi->spool);

                kfree(sbi);
        }
}

static inline int hugetlbfs_dec_free_inodes(struct hugetlbfs_sb_info *sbinfo)
{
        if (sbinfo->free_inodes >= 0) {
                spin_lock(&sbinfo->stat_lock);
                if (unlikely(!sbinfo->free_inodes)) {
                        spin_unlock(&sbinfo->stat_lock);
                        return 0;
                }
                sbinfo->free_inodes--;
                spin_unlock(&sbinfo->stat_lock);
        }

        return 1;
}

static void hugetlbfs_inc_free_inodes(struct hugetlbfs_sb_info *sbinfo)
{
        if (sbinfo->free_inodes >= 0) {
                spin_lock(&sbinfo->stat_lock);
                sbinfo->free_inodes++;
                spin_unlock(&sbinfo->stat_lock);
        }
}


static struct kmem_cache *hugetlbfs_inode_cachep;

static struct inode *hugetlbfs_alloc_inode(struct super_block *sb)
{
        struct hugetlbfs_sb_info *sbinfo = HUGETLBFS_SB(sb);
        struct hugetlbfs_inode_info *p;

        if (unlikely(!hugetlbfs_dec_free_inodes(sbinfo)))

                return NULL;
        p = kmem_cache_alloc(hugetlbfs_inode_cachep, GFP_KERNEL);
        if (unlikely(!p)) {
                hugetlbfs_inc_free_inodes(sbinfo);
                return NULL;
        }

        /*
         * Any time after allocation, hugetlbfs_destroy_inode can be called
         * for the inode.  mpol_free_shared_policy is unconditionally called
         * as part of hugetlbfs_destroy_inode.  So, initialize policy here
         * in case of a quick call to destroy.
         *
         * Note that the policy is initialized even if we are creating a
         * private inode.  This simplifies hugetlbfs_destroy_inode.
         */
        mpol_shared_policy_init(&p->policy, NULL);

        return &p->vfs_inode;
}

static void hugetlbfs_i_callback(struct rcu_head *head)
{
        struct inode *inode = container_of(head, struct inode, i_rcu);
        kmem_cache_free(hugetlbfs_inode_cachep, HUGETLBFS_I(inode));
}

static void hugetlbfs_destroy_inode(struct inode *inode)
{
        hugetlbfs_inc_free_inodes(HUGETLBFS_SB(inode->i_sb));
        mpol_free_shared_policy(&HUGETLBFS_I(inode)->policy);
        call_rcu(&inode->i_rcu, hugetlbfs_i_callback);
}

static const struct address_space_operations hugetlbfs_aops = {
        .write_begin    = hugetlbfs_write_begin,
        .write_end      = hugetlbfs_write_end,
        .set_page_dirty = hugetlbfs_set_page_dirty,
        .migratepage    = hugetlbfs_migrate_page,
        .error_remove_page      = hugetlbfs_error_remove_page,
};


static void init_once(void *foo)
{
        struct hugetlbfs_inode_info *ei = (struct hugetlbfs_inode_info *)foo;

        inode_init_once(&ei->vfs_inode);
}

const struct file_operations hugetlbfs_file_operations = {
        .read_iter              = hugetlbfs_read_iter,
        .mmap                   = hugetlbfs_file_mmap,
        .fsync                  = noop_fsync,
        .get_unmapped_area      = hugetlb_get_unmapped_area,
        .llseek                 = default_llseek,
        .fallocate              = hugetlbfs_fallocate,
};

static const struct inode_operations hugetlbfs_dir_inode_operations = {
        .create         = hugetlbfs_create,
        .lookup         = simple_lookup,
        .link           = simple_link,
        .unlink         = simple_unlink,
        .symlink        = hugetlbfs_symlink,
        .mkdir          = hugetlbfs_mkdir,
        .rmdir          = simple_rmdir,
        .mknod          = hugetlbfs_mknod,
        .rename         = simple_rename,
        .setattr        = hugetlbfs_setattr,
};

static const struct inode_operations hugetlbfs_inode_operations = {
        .setattr        = hugetlbfs_setattr,
};

static const struct super_operations hugetlbfs_ops = {
        .alloc_inode    = hugetlbfs_alloc_inode,
        .destroy_inode  = hugetlbfs_destroy_inode,
        .evict_inode    = hugetlbfs_evict_inode,
        .statfs         = hugetlbfs_statfs,
        .put_super      = hugetlbfs_put_super,
        .show_options   = hugetlbfs_show_options,
};

enum hugetlbfs_size_type { NO_SIZE, SIZE_STD, SIZE_PERCENT };

/*
 * Convert size option passed from command line to number of huge pages
 * in the pool specified by hstate.  Size option could be in bytes
 * (val_type == SIZE_STD) or percentage of the pool (val_type == SIZE_PERCENT).
 */
static long
hugetlbfs_size_to_hpages(struct hstate *h, unsigned long long size_opt,
                         enum hugetlbfs_size_type val_type)
{
        if (val_type == NO_SIZE)
                return -1;

        if (val_type == SIZE_PERCENT) {
                size_opt <<= huge_page_shift(h);
                size_opt *= h->max_huge_pages;
                do_div(size_opt, 100);
        }

        size_opt >>= huge_page_shift(h);
        return size_opt;
}

static int
hugetlbfs_parse_options(char *options, struct hugetlbfs_config *pconfig)
{
        char *p, *rest;
        substring_t args[MAX_OPT_ARGS];
        int option;
        unsigned long long max_size_opt = 0, min_size_opt = 0;
        enum hugetlbfs_size_type max_val_type = NO_SIZE, min_val_type = NO_SIZE;

        if (!options)
                return 0;

        while ((p = strsep(&options, ",")) != NULL) {
                int token;
                if (!*p)
                        continue;

                token = match_token(p, tokens, args);
                switch (token) {
                case Opt_uid:
                        if (match_int(&args[0], &option))
                                goto bad_val;
                        pconfig->uid = make_kuid(current_user_ns(), option);
                        if (!uid_valid(pconfig->uid))
                                goto bad_val;
                        break;

                case Opt_gid:
                        if (match_int(&args[0], &option))
                                goto bad_val;
                        pconfig->gid = make_kgid(current_user_ns(), option);
                        if (!gid_valid(pconfig->gid))
                                goto bad_val;
                        break;

                case Opt_mode:
                        if (match_octal(&args[0], &option))
                                goto bad_val;
                        pconfig->mode = option & 01777U;
                        break;

                case Opt_size: {
                        /* memparse() will accept a K/M/G without a digit */
                        if (!isdigit(*args[0].from))
                                goto bad_val;
                        max_size_opt = memparse(args[0].from, &rest);
                        max_val_type = SIZE_STD;
                        if (*rest == '%')
                                max_val_type = SIZE_PERCENT;
                        break;
                }

                case Opt_nr_inodes:
                        /* memparse() will accept a K/M/G without a digit */
                        if (!isdigit(*args[0].from))
                                goto bad_val;
                        pconfig->nr_inodes = memparse(args[0].from, &rest);
                        break;

                case Opt_pagesize: {
                        unsigned long ps;
                        ps = memparse(args[0].from, &rest);
                        pconfig->hstate = size_to_hstate(ps);
                        if (!pconfig->hstate) {
                                pr_err("Unsupported page size %lu MB\n",
                                        ps >> 20);
                                return -EINVAL;
                        }
                        break;
                }

                case Opt_min_size: {
                        /* memparse() will accept a K/M/G without a digit */
                        if (!isdigit(*args[0].from))
                                goto bad_val;
                        min_size_opt = memparse(args[0].from, &rest);
                        min_val_type = SIZE_STD;
                        if (*rest == '%')
                                min_val_type = SIZE_PERCENT;
                        break;
                }

                default:
                        pr_err("Bad mount option: \"%s\"\n", p);
                        return -EINVAL;
                        break;
                }
        }

        /*
         * Use huge page pool size (in hstate) to convert the size
         * options to number of huge pages.  If NO_SIZE, -1 is returned.
         */
        pconfig->max_hpages = hugetlbfs_size_to_hpages(pconfig->hstate,
                                                max_size_opt, max_val_type);
        pconfig->min_hpages = hugetlbfs_size_to_hpages(pconfig->hstate,
                                                min_size_opt, min_val_type);

        /*
         * If max_size was specified, then min_size must be smaller
         */
        if (max_val_type > NO_SIZE &&
            pconfig->min_hpages > pconfig->max_hpages) {
                pr_err("minimum size can not be greater than maximum size\n");
                return -EINVAL;
        }

        return 0;

bad_val:
        pr_err("Bad value '%s' for mount option '%s'\n", args[0].from, p);
        return -EINVAL;
}

static int
hugetlbfs_fill_super(struct super_block *sb, void *data, int silent)
{
        int ret;
        struct hugetlbfs_config config;
        struct hugetlbfs_sb_info *sbinfo;

        config.max_hpages = -1; /* No limit on size by default */
        config.nr_inodes = -1; /* No limit on number of inodes by default */
        config.uid = current_fsuid();
        config.gid = current_fsgid();
        config.mode = 0755;
        config.hstate = &default_hstate;
        config.min_hpages = -1; /* No default minimum size */
        ret = hugetlbfs_parse_options(data, &config);
        if (ret)
                return ret;

        sbinfo = kmalloc(sizeof(struct hugetlbfs_sb_info), GFP_KERNEL);
        if (!sbinfo)
                return -ENOMEM;
        sb->s_fs_info = sbinfo;
        sbinfo->hstate = config.hstate;
        spin_lock_init(&sbinfo->stat_lock);
        sbinfo->max_inodes = config.nr_inodes;
        sbinfo->free_inodes = config.nr_inodes;
        sbinfo->spool = NULL;
        sbinfo->uid = config.uid;
        sbinfo->gid = config.gid;
        sbinfo->mode = config.mode;

        /*
         * Allocate and initialize subpool if maximum or minimum size is
         * specified.  Any needed reservations (for minimim size) are taken
         * taken when the subpool is created.
         */
        if (config.max_hpages != -1 || config.min_hpages != -1) {
                sbinfo->spool = hugepage_new_subpool(config.hstate,
                                                        config.max_hpages,
                                                        config.min_hpages);
                if (!sbinfo->spool)
                        goto out_free;
        }
        sb->s_maxbytes = MAX_LFS_FILESIZE;
        sb->s_blocksize = huge_page_size(config.hstate);
        sb->s_blocksize_bits = huge_page_shift(config.hstate);
        sb->s_magic = HUGETLBFS_MAGIC;
        sb->s_op = &hugetlbfs_ops;
        sb->s_time_gran = 1;
        sb->s_root = d_make_root(hugetlbfs_get_root(sb, &config));
        if (!sb->s_root)
                goto out_free;
        return 0;
out_free:
        kfree(sbinfo->spool);
        kfree(sbinfo);
        return -ENOMEM;
}

static struct dentry *hugetlbfs_mount(struct file_system_type *fs_type,
        int flags, const char *dev_name, void *data)
{
        return mount_nodev(fs_type, flags, data, hugetlbfs_fill_super);
}

static struct file_system_type hugetlbfs_fs_type = {
        .name           = "hugetlbfs",
        .mount          = hugetlbfs_mount,
        .kill_sb        = kill_litter_super,
};

static struct vfsmount *hugetlbfs_vfsmount[HUGE_MAX_HSTATE];

static int can_do_hugetlb_shm(void)
{
        kgid_t shm_group;
        shm_group = make_kgid(&init_user_ns, sysctl_hugetlb_shm_group);
        return capable(CAP_IPC_LOCK) || in_group_p(shm_group);
}

static int get_hstate_idx(int page_size_log)
{
        struct hstate *h = hstate_sizelog(page_size_log);

        if (!h)
                return -1;
        return h - hstates;
}

static const struct dentry_operations anon_ops = {
        .d_dname = simple_dname
};

/*
 * Note that size should be aligned to proper hugepage size in caller side,
 * otherwise hugetlb_reserve_pages reserves one less hugepages than intended.
 */
struct file *hugetlb_file_setup(const char *name, size_t size,
                                vm_flags_t acctflag, struct user_struct **user,
                                int creat_flags, int page_size_log)
{
        struct file *file = ERR_PTR(-ENOMEM);
        struct inode *inode;
        struct path path;
        struct super_block *sb;
        struct qstr quick_string;
        int hstate_idx;

        hstate_idx = get_hstate_idx(page_size_log);
        if (hstate_idx < 0)
                return ERR_PTR(-ENODEV);

        *user = NULL;
        if (!hugetlbfs_vfsmount[hstate_idx])
                return ERR_PTR(-ENOENT);

        if (creat_flags == HUGETLB_SHMFS_INODE && !can_do_hugetlb_shm()) {
                *user = current_user();
                if (user_shm_lock(size, *user)) {
                        task_lock(current);
                        pr_warn_once("%s (%d): Using mlock ulimits for SHM_HUGETLB is deprecated\n",
                                current->comm, current->pid);
                        task_unlock(current);
                } else {
                        *user = NULL;
                        return ERR_PTR(-EPERM);
                }
        }

        sb = hugetlbfs_vfsmount[hstate_idx]->mnt_sb;
        quick_string.name = name;
        quick_string.len = strlen(quick_string.name);
        quick_string.hash = 0;
        path.dentry = d_alloc_pseudo(sb, &quick_string);
        if (!path.dentry)
                goto out_shm_unlock;

        d_set_d_op(path.dentry, &anon_ops);
        path.mnt = mntget(hugetlbfs_vfsmount[hstate_idx]);
        file = ERR_PTR(-ENOSPC);
        inode = hugetlbfs_get_inode(sb, NULL, S_IFREG | S_IRWXUGO, 0);
        if (!inode)
                goto out_dentry;
        if (creat_flags == HUGETLB_SHMFS_INODE)
                inode->i_flags |= S_PRIVATE;

        file = ERR_PTR(-ENOMEM);
        if (hugetlb_reserve_pages(inode, 0,
                        size >> huge_page_shift(hstate_inode(inode)), NULL,
                        acctflag))
                goto out_inode;

        d_instantiate(path.dentry, inode);
        inode->i_size = size;
        clear_nlink(inode);

        file = alloc_file(&path, FMODE_WRITE | FMODE_READ,
                        &hugetlbfs_file_operations);
        if (IS_ERR(file))
                goto out_dentry; /* inode is already attached */

        return file;

out_inode:
        iput(inode);
out_dentry:
        path_put(&path);
out_shm_unlock:
        if (*user) {
                user_shm_unlock(size, *user);
                *user = NULL;
        }
        return file;
}

static int __init init_hugetlbfs_fs(void)
{
        struct hstate *h;
        int error;
        int i;

        if (!hugepages_supported()) {
                pr_info("disabling because there are no supported hugepage sizes\n");
                return -ENOTSUPP;
        }

        error = -ENOMEM;
        hugetlbfs_inode_cachep = kmem_cache_create("hugetlbfs_inode_cache",
                                        sizeof(struct hugetlbfs_inode_info),
                                        0, SLAB_ACCOUNT, init_once);
        if (hugetlbfs_inode_cachep == NULL)
                goto out2;

        error = register_filesystem(&hugetlbfs_fs_type);
        if (error)
                goto out;

        i = 0;
        for_each_hstate(h) {
                char buf[50];
                unsigned ps_kb = 1U << (h->order + PAGE_SHIFT - 10);

                snprintf(buf, sizeof(buf), "pagesize=%uK", ps_kb);
                hugetlbfs_vfsmount[i] = kern_mount_data(&hugetlbfs_fs_type,
                                                        buf);

                if (IS_ERR(hugetlbfs_vfsmount[i])) {
                        pr_err("Cannot mount internal hugetlbfs for "
                                "page size %uK", ps_kb);
                        error = PTR_ERR(hugetlbfs_vfsmount[i]);
                        hugetlbfs_vfsmount[i] = NULL;
                }
                i++;
        }
        /* Non default hstates are optional */
        if (!IS_ERR_OR_NULL(hugetlbfs_vfsmount[default_hstate_idx]))
                return 0;

 out:
        kmem_cache_destroy(hugetlbfs_inode_cachep);
 out2:
        return error;
}
fs_initcall(init_hugetlbfs_fs)