/*
 *      linux/mm/filemap_xip.c
 *
 * Copyright (C) 2005 IBM Corporation
 * Author: Carsten Otte <cotte@de.ibm.com>
 *
 * derived from linux/mm/filemap.c - Copyright (C) Linus Torvalds
 *
 */

#include <linux/fs.h>
#include <linux/pagemap.h>
#include <linux/module.h>
#include <linux/uio.h>
#include <linux/rmap.h>
#include <linux/sched.h>
#include <asm/tlbflush.h>

/*
 * We do use our own empty page to avoid interference with other users
 * of ZERO_PAGE(), such as /dev/zero
 */
static struct page *__xip_sparse_page;

static struct page *xip_sparse_page(void)
{
        if (!__xip_sparse_page) {
                struct page *page = alloc_page(GFP_HIGHUSER | __GFP_ZERO);

                if (page) {
                        static DEFINE_SPINLOCK(xip_alloc_lock);
                        spin_lock(&xip_alloc_lock);
                        if (!__xip_sparse_page)
                                __xip_sparse_page = page;
                        else
                                __free_page(page);
                        spin_unlock(&xip_alloc_lock);
                }
        }
        return __xip_sparse_page;
}

/*
 * This is a file read routine for execute in place files, and uses
 * the mapping->a_ops->get_xip_page() function for the actual low-level
 * stuff.
 *
 * Note the struct file* is not used at all.  It may be NULL.
 */
static void
do_xip_mapping_read(struct address_space *mapping,
                    struct file_ra_state *_ra,
                    struct file *filp,
                    loff_t *ppos,
                    read_descriptor_t *desc,
                    read_actor_t actor)
{
        struct inode *inode = mapping->host;
        unsigned long index, end_index, offset;
        loff_t isize;

        BUG_ON(!mapping->a_ops->get_xip_page);

        index = *ppos >> PAGE_CACHE_SHIFT;
        offset = *ppos & ~PAGE_CACHE_MASK;

        isize = i_size_read(inode);
        if (!isize)
                goto out;

        end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
        for (;;) {
                struct page *page;
                unsigned long nr, ret;

                /* nr is the maximum number of bytes to copy from this page */
                nr = PAGE_CACHE_SIZE;
                if (index >= end_index) {
                        if (index > end_index)
                                goto out;
                        nr = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
                        if (nr <= offset) {
                                goto out;
                        }
                }
                nr = nr - offset;

                page = mapping->a_ops->get_xip_page(mapping,
                        index*(PAGE_SIZE/512), 0);
                if (!page)
                        goto no_xip_page;
                if (unlikely(IS_ERR(page))) {
                        if (PTR_ERR(page) == -ENODATA) {
                                /* sparse */
                                page = ZERO_PAGE(0);
                        } else {
                                desc->error = PTR_ERR(page);
                                goto out;
                        }
                }

                /* If users can be writing to this page using arbitrary
                 * virtual addresses, take care about potential aliasing
                 * before reading the page on the kernel side.
                 */
                if (mapping_writably_mapped(mapping))
                        flush_dcache_page(page);

                /*
                 * Ok, we have the page, so now we can copy it to user space...
                 *
                 * The actor routine returns how many bytes were actually used..
                 * NOTE! This may not be the same as how much of a user buffer
                 * we filled up (we may be padding etc), so we can only update
                 * "pos" here (the actor routine has to update the user buffer
                 * pointers and the remaining count).
                 */
                ret = actor(desc, page, offset, nr);
                offset += ret;
                index += offset >> PAGE_CACHE_SHIFT;
                offset &= ~PAGE_CACHE_MASK;

                if (ret == nr && desc->count)
                        continue;
                goto out;

no_xip_page:
                /* Did not get the page. Report it */
                desc->error = -EIO;
                goto out;
        }

out:
        *ppos = ((loff_t) index << PAGE_CACHE_SHIFT) + offset;
        if (filp)
                file_accessed(filp);
}

ssize_t
xip_file_read(struct file *filp, char __user *buf, size_t len, loff_t *ppos)
{
        read_descriptor_t desc;

        if (!access_ok(VERIFY_WRITE, buf, len))
                return -EFAULT;

        desc.written = 0;
        desc.arg.buf = buf;
        desc.count = len;
        desc.error = 0;

        do_xip_mapping_read(filp->f_mapping, &filp->f_ra, filp,
                            ppos, &desc, file_read_actor);

        if (desc.written)
                return desc.written;
        else
                return desc.error;
}
EXPORT_SYMBOL_GPL(xip_file_read);

/*
 * __xip_unmap is invoked from xip_unmap and
 * xip_write
 *
 * This function walks all vmas of the address_space and unmaps the
 * __xip_sparse_page when found at pgoff.
 */
static void
__xip_unmap (struct address_space * mapping,
                     unsigned long pgoff)
{
        struct vm_area_struct *vma;
        struct mm_struct *mm;
        struct prio_tree_iter iter;
        unsigned long address;
        pte_t *pte;
        pte_t pteval;
        spinlock_t *ptl;
        struct page *page;

        page = __xip_sparse_page;
        if (!page)
                return;

        spin_lock(&mapping->i_mmap_lock);
        vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
                mm = vma->vm_mm;
                address = vma->vm_start +
                        ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
                BUG_ON(address < vma->vm_start || address >= vma->vm_end);
                pte = page_check_address(page, mm, address, &ptl);
                if (pte) {
                        /* Nuke the page table entry. */
                        flush_cache_page(vma, address, pte_pfn(*pte));
                        pteval = ptep_clear_flush(vma, address, pte);
                        page_remove_rmap(page, vma);
                        dec_mm_counter(mm, file_rss);
                        BUG_ON(pte_dirty(pteval));
                        pte_unmap_unlock(pte, ptl);
                        page_cache_release(page);
                }
        }
        spin_unlock(&mapping->i_mmap_lock);
}

/*
 * xip_fault() is invoked via the vma operations vector for a
 * mapped memory region to read in file data during a page fault.
 *
 * This function is derived from filemap_fault, but used for execute in place
 */
static int xip_file_fault(struct vm_area_struct *area, struct vm_fault *vmf)
{
        struct file *file = area->vm_file;
        struct address_space *mapping = file->f_mapping;
        struct inode *inode = mapping->host;
        struct page *page;
        pgoff_t size;

        /* XXX: are VM_FAULT_ codes OK? */

        size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
        if (vmf->pgoff >= size)
                return VM_FAULT_SIGBUS;

        page = mapping->a_ops->get_xip_page(mapping,
                                        vmf->pgoff*(PAGE_SIZE/512), 0);
        if (!IS_ERR(page))
                goto out;
        if (PTR_ERR(page) != -ENODATA)
                return VM_FAULT_OOM;

        /* sparse block */
        if ((area->vm_flags & (VM_WRITE | VM_MAYWRITE)) &&
            (area->vm_flags & (VM_SHARED| VM_MAYSHARE)) &&
            (!(mapping->host->i_sb->s_flags & MS_RDONLY))) {
                /* maybe shared writable, allocate new block */
                page = mapping->a_ops->get_xip_page(mapping,
                                        vmf->pgoff*(PAGE_SIZE/512), 1);
                if (IS_ERR(page))
                        return VM_FAULT_SIGBUS;
                /* unmap page at pgoff from all other vmas */
                __xip_unmap(mapping, vmf->pgoff);
        } else {
                /* not shared and writable, use xip_sparse_page() */
                page = xip_sparse_page();
                if (!page)
                        return VM_FAULT_OOM;
        }

out:
        page_cache_get(page);
        vmf->page = page;
        return 0;
}

static struct vm_operations_struct xip_file_vm_ops = {
        .fault  = xip_file_fault,
};

int xip_file_mmap(struct file * file, struct vm_area_struct * vma)
{
        BUG_ON(!file->f_mapping->a_ops->get_xip_page);

        file_accessed(file);
        vma->vm_ops = &xip_file_vm_ops;
        vma->vm_flags |= VM_CAN_NONLINEAR;
        return 0;
}
EXPORT_SYMBOL_GPL(xip_file_mmap);

static ssize_t
__xip_file_write(struct file *filp, const char __user *buf,
                  size_t count, loff_t pos, loff_t *ppos)
{
        struct address_space * mapping = filp->f_mapping;
        const struct address_space_operations *a_ops = mapping->a_ops;
        struct inode    *inode = mapping->host;
        long            status = 0;
        struct page     *page;
        size_t          bytes;
        ssize_t         written = 0;

        BUG_ON(!mapping->a_ops->get_xip_page);

        do {
                unsigned long index;
                unsigned long offset;
                size_t copied;
                char *kaddr;

                offset = (pos & (PAGE_CACHE_SIZE -1)); /* Within page */
                index = pos >> PAGE_CACHE_SHIFT;
                bytes = PAGE_CACHE_SIZE - offset;
                if (bytes > count)
                        bytes = count;

                page = a_ops->get_xip_page(mapping,
                                           index*(PAGE_SIZE/512), 0);
                if (IS_ERR(page) && (PTR_ERR(page) == -ENODATA)) {
                        /* we allocate a new page unmap it */
                        page = a_ops->get_xip_page(mapping,
                                                   index*(PAGE_SIZE/512), 1);
                        if (!IS_ERR(page))
                                /* unmap page at pgoff from all other vmas */
                                __xip_unmap(mapping, index);
                }

                if (IS_ERR(page)) {
                        status = PTR_ERR(page);
                        break;
                }

                fault_in_pages_readable(buf, bytes);
                kaddr = kmap_atomic(page, KM_USER0);
                copied = bytes -
                        __copy_from_user_inatomic_nocache(kaddr + offset, buf, bytes);
                kunmap_atomic(kaddr, KM_USER0);
                flush_dcache_page(page);

                if (likely(copied > 0)) {
                        status = copied;

                        if (status >= 0) {
                                written += status;
                                count -= status;
                                pos += status;
                                buf += status;
                        }
                }
                if (unlikely(copied != bytes))
                        if (status >= 0)
                                status = -EFAULT;
                if (status < 0)
                        break;
        } while (count);
        *ppos = pos;
        /*
         * No need to use i_size_read() here, the i_size
         * cannot change under us because we hold i_mutex.
         */
        if (pos > inode->i_size) {
                i_size_write(inode, pos);
                mark_inode_dirty(inode);
        }

        return written ? written : status;
}

ssize_t
xip_file_write(struct file *filp, const char __user *buf, size_t len,
               loff_t *ppos)
{
        struct address_space *mapping = filp->f_mapping;
        struct inode *inode = mapping->host;
        size_t count;
        loff_t pos;
        ssize_t ret;

        mutex_lock(&inode->i_mutex);

        if (!access_ok(VERIFY_READ, buf, len)) {
                ret=-EFAULT;
                goto out_up;
        }

        pos = *ppos;
        count = len;

        vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);

        /* We can write back this queue in page reclaim */
        current->backing_dev_info = mapping->backing_dev_info;

        ret = generic_write_checks(filp, &pos, &count, S_ISBLK(inode->i_mode));
        if (ret)
                goto out_backing;
        if (count == 0)
                goto out_backing;

        ret = remove_suid(filp->f_path.dentry);
        if (ret)
                goto out_backing;

        file_update_time(filp);

        ret = __xip_file_write (filp, buf, count, pos, ppos);

 out_backing:
        current->backing_dev_info = NULL;
 out_up:
        mutex_unlock(&inode->i_mutex);
        return ret;
}
EXPORT_SYMBOL_GPL(xip_file_write);

/*
 * truncate a page used for execute in place
 * functionality is analog to block_truncate_page but does use get_xip_page
 * to get the page instead of page cache
 */
int
xip_truncate_page(struct address_space *mapping, loff_t from)
{
        pgoff_t index = from >> PAGE_CACHE_SHIFT;
        unsigned offset = from & (PAGE_CACHE_SIZE-1);
        unsigned blocksize;
        unsigned length;
        struct page *page;

        BUG_ON(!mapping->a_ops->get_xip_page);

        blocksize = 1 << mapping->host->i_blkbits;
        length = offset & (blocksize - 1);

        /* Block boundary? Nothing to do */
        if (!length)
                return 0;

        length = blocksize - length;

        page = mapping->a_ops->get_xip_page(mapping,
                                            index*(PAGE_SIZE/512), 0);
        if (!page)
                return -ENOMEM;
        if (unlikely(IS_ERR(page))) {
                if (PTR_ERR(page) == -ENODATA)
                        /* Hole? No need to truncate */
                        return 0;
                else
                        return PTR_ERR(page);
        }
        zero_user_page(page, offset, length, KM_USER0);
        return 0;
}
EXPORT_SYMBOL_GPL(xip_truncate_page);