// SPDX-License-Identifier: GPL-2.0
/*
 *  linux/fs/ext4/file.c
 *
 * Copyright (C) 1992, 1993, 1994, 1995
 * Remy Card (card@masi.ibp.fr)
 * Laboratoire MASI - Institut Blaise Pascal
 * Universite Pierre et Marie Curie (Paris VI)
 *
 *  from
 *
 *  linux/fs/minix/file.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  ext4 fs regular file handling primitives
 *
 *  64-bit file support on 64-bit platforms by Jakub Jelinek
 *      (jj@sunsite.ms.mff.cuni.cz)
 */

#include <linux/time.h>
#include <linux/fs.h>
#include <linux/iomap.h>
#include <linux/mount.h>
#include <linux/path.h>
#include <linux/dax.h>
#include <linux/quotaops.h>
#include <linux/pagevec.h>
#include <linux/uio.h>
#include <linux/mman.h>
#include <linux/backing-dev.h>
#include "ext4.h"
#include "ext4_jbd2.h"
#include "xattr.h"
#include "acl.h"
#include "truncate.h"

static bool ext4_dio_supported(struct inode *inode)
{
        if (IS_ENABLED(CONFIG_FS_ENCRYPTION) && IS_ENCRYPTED(inode))
                return false;
        if (fsverity_active(inode))
                return false;
        if (ext4_should_journal_data(inode))
                return false;
        if (ext4_has_inline_data(inode))
                return false;
        return true;
}

static ssize_t ext4_dio_read_iter(struct kiocb *iocb, struct iov_iter *to)
{
        ssize_t ret;
        struct inode *inode = file_inode(iocb->ki_filp);

        if (iocb->ki_flags & IOCB_NOWAIT) {
                if (!inode_trylock_shared(inode))
                        return -EAGAIN;
        } else {
                inode_lock_shared(inode);
        }

        if (!ext4_dio_supported(inode)) {
                inode_unlock_shared(inode);
                /*
                 * Fallback to buffered I/O if the operation being performed on
                 * the inode is not supported by direct I/O. The IOCB_DIRECT
                 * flag needs to be cleared here in order to ensure that the
                 * direct I/O path within generic_file_read_iter() is not
                 * taken.
                 */
                iocb->ki_flags &= ~IOCB_DIRECT;
                return generic_file_read_iter(iocb, to);
        }

        ret = iomap_dio_rw(iocb, to, &ext4_iomap_ops, NULL,
                           is_sync_kiocb(iocb));
        inode_unlock_shared(inode);

        file_accessed(iocb->ki_filp);
        return ret;
}

#ifdef CONFIG_FS_DAX
static ssize_t ext4_dax_read_iter(struct kiocb *iocb, struct iov_iter *to)
{
        struct inode *inode = file_inode(iocb->ki_filp);
        ssize_t ret;

        if (iocb->ki_flags & IOCB_NOWAIT) {
                if (!inode_trylock_shared(inode))
                        return -EAGAIN;
        } else {
                inode_lock_shared(inode);
        }
        /*
         * Recheck under inode lock - at this point we are sure it cannot
         * change anymore
         */
        if (!IS_DAX(inode)) {
                inode_unlock_shared(inode);
                /* Fallback to buffered IO in case we cannot support DAX */
                return generic_file_read_iter(iocb, to);
        }
        ret = dax_iomap_rw(iocb, to, &ext4_iomap_ops);
        inode_unlock_shared(inode);

        file_accessed(iocb->ki_filp);
        return ret;
}
#endif

static ssize_t ext4_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
{
        struct inode *inode = file_inode(iocb->ki_filp);

        if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb))))
                return -EIO;

        if (!iov_iter_count(to))
                return 0; /* skip atime */

#ifdef CONFIG_FS_DAX
        if (IS_DAX(inode))
                return ext4_dax_read_iter(iocb, to);
#endif
        if (iocb->ki_flags & IOCB_DIRECT)
                return ext4_dio_read_iter(iocb, to);

        return generic_file_read_iter(iocb, to);
}

/*
 * Called when an inode is released. Note that this is different
 * from ext4_file_open: open gets called at every open, but release
 * gets called only when /all/ the files are closed.
 */
static int ext4_release_file(struct inode *inode, struct file *filp)
{
        if (ext4_test_inode_state(inode, EXT4_STATE_DA_ALLOC_CLOSE)) {
                ext4_alloc_da_blocks(inode);
                ext4_clear_inode_state(inode, EXT4_STATE_DA_ALLOC_CLOSE);
        }
        /* if we are the last writer on the inode, drop the block reservation */
        if ((filp->f_mode & FMODE_WRITE) &&
                        (atomic_read(&inode->i_writecount) == 1) &&
                        !EXT4_I(inode)->i_reserved_data_blocks) {
                down_write(&EXT4_I(inode)->i_data_sem);
                ext4_discard_preallocations(inode, 0);
                up_write(&EXT4_I(inode)->i_data_sem);
        }
        if (is_dx(inode) && filp->private_data)
                ext4_htree_free_dir_info(filp->private_data);

        return 0;
}

/*
 * This tests whether the IO in question is block-aligned or not.
 * Ext4 utilizes unwritten extents when hole-filling during direct IO, and they
 * are converted to written only after the IO is complete.  Until they are
 * mapped, these blocks appear as holes, so dio_zero_block() will assume that
 * it needs to zero out portions of the start and/or end block.  If 2 AIO
 * threads are at work on the same unwritten block, they must be synchronized
 * or one thread will zero the other's data, causing corruption.
 */
static bool
ext4_unaligned_io(struct inode *inode, struct iov_iter *from, loff_t pos)
{
        struct super_block *sb = inode->i_sb;
        unsigned long blockmask = sb->s_blocksize - 1;

        if ((pos | iov_iter_alignment(from)) & blockmask)
                return true;

        return false;
}

static bool
ext4_extending_io(struct inode *inode, loff_t offset, size_t len)
{
        if (offset + len > i_size_read(inode) ||
            offset + len > EXT4_I(inode)->i_disksize)
                return true;
        return false;
}

/* Is IO overwriting allocated and initialized blocks? */
static bool ext4_overwrite_io(struct inode *inode, loff_t pos, loff_t len)
{
        struct ext4_map_blocks map;
        unsigned int blkbits = inode->i_blkbits;
        int err, blklen;

        if (pos + len > i_size_read(inode))
                return false;

        map.m_lblk = pos >> blkbits;
        map.m_len = EXT4_MAX_BLOCKS(len, pos, blkbits);
        blklen = map.m_len;

        err = ext4_map_blocks(NULL, inode, &map, 0);
        /*
         * 'err==len' means that all of the blocks have been preallocated,
         * regardless of whether they have been initialized or not. To exclude
         * unwritten extents, we need to check m_flags.
         */
        return err == blklen && (map.m_flags & EXT4_MAP_MAPPED);
}

static ssize_t ext4_generic_write_checks(struct kiocb *iocb,
                                         struct iov_iter *from)
{
        struct inode *inode = file_inode(iocb->ki_filp);
        ssize_t ret;

        if (unlikely(IS_IMMUTABLE(inode)))
                return -EPERM;

        ret = generic_write_checks(iocb, from);
        if (ret <= 0)
                return ret;

        /*
         * If we have encountered a bitmap-format file, the size limit
         * is smaller than s_maxbytes, which is for extent-mapped files.
         */
        if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))) {
                struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);

                if (iocb->ki_pos >= sbi->s_bitmap_maxbytes)
                        return -EFBIG;
                iov_iter_truncate(from, sbi->s_bitmap_maxbytes - iocb->ki_pos);
        }

        return iov_iter_count(from);
}

static ssize_t ext4_write_checks(struct kiocb *iocb, struct iov_iter *from)
{
        ssize_t ret, count;

        count = ext4_generic_write_checks(iocb, from);
        if (count <= 0)
                return count;

        ret = file_modified(iocb->ki_filp);
        if (ret)
                return ret;
        return count;
}

static ssize_t ext4_buffered_write_iter(struct kiocb *iocb,
                                        struct iov_iter *from)
{
        ssize_t ret;
        struct inode *inode = file_inode(iocb->ki_filp);

        if (iocb->ki_flags & IOCB_NOWAIT)
                return -EOPNOTSUPP;

        inode_lock(inode);
        ret = ext4_write_checks(iocb, from);
        if (ret <= 0)
                goto out;

        current->backing_dev_info = inode_to_bdi(inode);
        ret = generic_perform_write(iocb->ki_filp, from, iocb->ki_pos);
        current->backing_dev_info = NULL;

out:
        inode_unlock(inode);
        if (likely(ret > 0)) {
                iocb->ki_pos += ret;
                ret = generic_write_sync(iocb, ret);
        }

        return ret;
}

static ssize_t ext4_handle_inode_extension(struct inode *inode, loff_t offset,
                                           ssize_t written, size_t count)
{
        handle_t *handle;
        bool truncate = false;
        u8 blkbits = inode->i_blkbits;
        ext4_lblk_t written_blk, end_blk;
        int ret;

        /*
         * Note that EXT4_I(inode)->i_disksize can get extended up to
         * inode->i_size while the I/O was running due to writeback of delalloc
         * blocks. But, the code in ext4_iomap_alloc() is careful to use
         * zeroed/unwritten extents if this is possible; thus we won't leave
         * uninitialized blocks in a file even if we didn't succeed in writing
         * as much as we intended.
         */
        WARN_ON_ONCE(i_size_read(inode) < EXT4_I(inode)->i_disksize);
        if (offset + count <= EXT4_I(inode)->i_disksize) {
                /*
                 * We need to ensure that the inode is removed from the orphan
                 * list if it has been added prematurely, due to writeback of
                 * delalloc blocks.
                 */
                if (!list_empty(&EXT4_I(inode)->i_orphan) && inode->i_nlink) {
                        handle = ext4_journal_start(inode, EXT4_HT_INODE, 2);

                        if (IS_ERR(handle)) {
                                ext4_orphan_del(NULL, inode);
                                return PTR_ERR(handle);
                        }

                        ext4_orphan_del(handle, inode);
                        ext4_journal_stop(handle);
                }

                return written;
        }

        if (written < 0)
                goto truncate;

        handle = ext4_journal_start(inode, EXT4_HT_INODE, 2);
        if (IS_ERR(handle)) {
                written = PTR_ERR(handle);
                goto truncate;
        }

        if (ext4_update_inode_size(inode, offset + written)) {
                ret = ext4_mark_inode_dirty(handle, inode);
                if (unlikely(ret)) {
                        written = ret;
                        ext4_journal_stop(handle);
                        goto truncate;
                }
        }

        /*
         * We may need to truncate allocated but not written blocks beyond EOF.
         */
        written_blk = ALIGN(offset + written, 1 << blkbits);
        end_blk = ALIGN(offset + count, 1 << blkbits);
        if (written_blk < end_blk && ext4_can_truncate(inode))
                truncate = true;

        /*
         * Remove the inode from the orphan list if it has been extended and
         * everything went OK.
         */
        if (!truncate && inode->i_nlink)
                ext4_orphan_del(handle, inode);
        ext4_journal_stop(handle);

        if (truncate) {
truncate:
                ext4_truncate_failed_write(inode);
                /*
                 * If the truncate operation failed early, then the inode may
                 * still be on the orphan list. In that case, we need to try
                 * remove the inode from the in-memory linked list.
                 */
                if (inode->i_nlink)
                        ext4_orphan_del(NULL, inode);
        }

        return written;
}

static int ext4_dio_write_end_io(struct kiocb *iocb, ssize_t size,
                                 int error, unsigned int flags)
{
        loff_t offset = iocb->ki_pos;
        struct inode *inode = file_inode(iocb->ki_filp);

        if (error)
                return error;

        if (size && flags & IOMAP_DIO_UNWRITTEN)
                return ext4_convert_unwritten_extents(NULL, inode,
                                                      offset, size);

        return 0;
}

static const struct iomap_dio_ops ext4_dio_write_ops = {
        .end_io = ext4_dio_write_end_io,
};

/*
 * The intention here is to start with shared lock acquired then see if any
 * condition requires an exclusive inode lock. If yes, then we restart the
 * whole operation by releasing the shared lock and acquiring exclusive lock.
 *
 * - For unaligned_io we never take shared lock as it may cause data corruption
 *   when two unaligned IO tries to modify the same block e.g. while zeroing.
 *
 * - For extending writes case we don't take the shared lock, since it requires
 *   updating inode i_disksize and/or orphan handling with exclusive lock.
 *
 * - shared locking will only be true mostly with overwrites. Otherwise we will
 *   switch to exclusive i_rwsem lock.
 */
static ssize_t ext4_dio_write_checks(struct kiocb *iocb, struct iov_iter *from,
                                     bool *ilock_shared, bool *extend)
{
        struct file *file = iocb->ki_filp;
        struct inode *inode = file_inode(file);
        loff_t offset;
        size_t count;
        ssize_t ret;

restart:
        ret = ext4_generic_write_checks(iocb, from);
        if (ret <= 0)
                goto out;

        offset = iocb->ki_pos;
        count = ret;
        if (ext4_extending_io(inode, offset, count))
                *extend = true;
        /*
         * Determine whether the IO operation will overwrite allocated
         * and initialized blocks.
         * We need exclusive i_rwsem for changing security info
         * in file_modified().
         */
        if (*ilock_shared && (!IS_NOSEC(inode) || *extend ||
             !ext4_overwrite_io(inode, offset, count))) {
                if (iocb->ki_flags & IOCB_NOWAIT) {
                        ret = -EAGAIN;
                        goto out;
                }
                inode_unlock_shared(inode);
                *ilock_shared = false;
                inode_lock(inode);
                goto restart;
        }

        ret = file_modified(file);
        if (ret < 0)
                goto out;

        return count;
out:
        if (*ilock_shared)
                inode_unlock_shared(inode);
        else
                inode_unlock(inode);
        return ret;
}

static ssize_t ext4_dio_write_iter(struct kiocb *iocb, struct iov_iter *from)
{
        ssize_t ret;
        handle_t *handle;
        struct inode *inode = file_inode(iocb->ki_filp);
        loff_t offset = iocb->ki_pos;
        size_t count = iov_iter_count(from);
        const struct iomap_ops *iomap_ops = &ext4_iomap_ops;
        bool extend = false, unaligned_io = false;
        bool ilock_shared = true;

        /*
         * We initially start with shared inode lock unless it is
         * unaligned IO which needs exclusive lock anyways.
         */
        if (ext4_unaligned_io(inode, from, offset)) {
                unaligned_io = true;
                ilock_shared = false;
        }
        /*
         * Quick check here without any i_rwsem lock to see if it is extending
         * IO. A more reliable check is done in ext4_dio_write_checks() with
         * proper locking in place.
         */
        if (offset + count > i_size_read(inode))
                ilock_shared = false;

        if (iocb->ki_flags & IOCB_NOWAIT) {
                if (ilock_shared) {
                        if (!inode_trylock_shared(inode))
                                return -EAGAIN;
                } else {
                        if (!inode_trylock(inode))
                                return -EAGAIN;
                }
        } else {
                if (ilock_shared)
                        inode_lock_shared(inode);
                else
                        inode_lock(inode);
        }

        /* Fallback to buffered I/O if the inode does not support direct I/O. */
        if (!ext4_dio_supported(inode)) {
                if (ilock_shared)
                        inode_unlock_shared(inode);
                else
                        inode_unlock(inode);
                return ext4_buffered_write_iter(iocb, from);
        }

        ret = ext4_dio_write_checks(iocb, from, &ilock_shared, &extend);
        if (ret <= 0)
                return ret;

        /* if we're going to block and IOCB_NOWAIT is set, return -EAGAIN */
        if ((iocb->ki_flags & IOCB_NOWAIT) && (unaligned_io || extend)) {
                ret = -EAGAIN;
                goto out;
        }

        offset = iocb->ki_pos;
        count = ret;

        /*
         * Unaligned direct IO must be serialized among each other as zeroing
         * of partial blocks of two competing unaligned IOs can result in data
         * corruption.
         *
         * So we make sure we don't allow any unaligned IO in flight.
         * For IOs where we need not wait (like unaligned non-AIO DIO),
         * below inode_dio_wait() may anyway become a no-op, since we start
         * with exclusive lock.
         */
        if (unaligned_io)
                inode_dio_wait(inode);

        if (extend) {
                handle = ext4_journal_start(inode, EXT4_HT_INODE, 2);
                if (IS_ERR(handle)) {
                        ret = PTR_ERR(handle);
                        goto out;
                }

                ret = ext4_orphan_add(handle, inode);
                if (ret) {
                        ext4_journal_stop(handle);
                        goto out;
                }

                ext4_journal_stop(handle);
        }

        if (ilock_shared)
                iomap_ops = &ext4_iomap_overwrite_ops;
        ret = iomap_dio_rw(iocb, from, iomap_ops, &ext4_dio_write_ops,
                           is_sync_kiocb(iocb) || unaligned_io || extend);
        if (ret == -ENOTBLK)
                ret = 0;

        if (extend)
                ret = ext4_handle_inode_extension(inode, offset, ret, count);

out:
        if (ilock_shared)
                inode_unlock_shared(inode);
        else
                inode_unlock(inode);

        if (ret >= 0 && iov_iter_count(from)) {
                ssize_t err;
                loff_t endbyte;

                offset = iocb->ki_pos;
                err = ext4_buffered_write_iter(iocb, from);
                if (err < 0)
                        return err;

                /*
                 * We need to ensure that the pages within the page cache for
                 * the range covered by this I/O are written to disk and
                 * invalidated. This is in attempt to preserve the expected
                 * direct I/O semantics in the case we fallback to buffered I/O
                 * to complete off the I/O request.
                 */
                ret += err;
                endbyte = offset + err - 1;
                err = filemap_write_and_wait_range(iocb->ki_filp->f_mapping,
                                                   offset, endbyte);
                if (!err)
                        invalidate_mapping_pages(iocb->ki_filp->f_mapping,
                                                 offset >> PAGE_SHIFT,
                                                 endbyte >> PAGE_SHIFT);
        }

        return ret;
}

#ifdef CONFIG_FS_DAX
static ssize_t
ext4_dax_write_iter(struct kiocb *iocb, struct iov_iter *from)
{
        ssize_t ret;
        size_t count;
        loff_t offset;
        handle_t *handle;
        bool extend = false;
        struct inode *inode = file_inode(iocb->ki_filp);

        if (iocb->ki_flags & IOCB_NOWAIT) {
                if (!inode_trylock(inode))
                        return -EAGAIN;
        } else {
                inode_lock(inode);
        }

        ret = ext4_write_checks(iocb, from);
        if (ret <= 0)
                goto out;

        offset = iocb->ki_pos;
        count = iov_iter_count(from);

        if (offset + count > EXT4_I(inode)->i_disksize) {
                handle = ext4_journal_start(inode, EXT4_HT_INODE, 2);
                if (IS_ERR(handle)) {
                        ret = PTR_ERR(handle);
                        goto out;
                }

                ret = ext4_orphan_add(handle, inode);
                if (ret) {
                        ext4_journal_stop(handle);
                        goto out;
                }

                extend = true;
                ext4_journal_stop(handle);
        }

        ret = dax_iomap_rw(iocb, from, &ext4_iomap_ops);

        if (extend)
                ret = ext4_handle_inode_extension(inode, offset, ret, count);
out:
        inode_unlock(inode);
        if (ret > 0)
                ret = generic_write_sync(iocb, ret);
        return ret;
}
#endif

static ssize_t
ext4_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
{
        struct inode *inode = file_inode(iocb->ki_filp);

        if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb))))
                return -EIO;

#ifdef CONFIG_FS_DAX
        if (IS_DAX(inode))
                return ext4_dax_write_iter(iocb, from);
#endif
        if (iocb->ki_flags & IOCB_DIRECT)
                return ext4_dio_write_iter(iocb, from);

        return ext4_buffered_write_iter(iocb, from);
}

#ifdef CONFIG_FS_DAX
static vm_fault_t ext4_dax_huge_fault(struct vm_fault *vmf,
                enum page_entry_size pe_size)
{
        int error = 0;
        vm_fault_t result;
        int retries = 0;
        handle_t *handle = NULL;
        struct inode *inode = file_inode(vmf->vma->vm_file);
        struct super_block *sb = inode->i_sb;

        /*
         * We have to distinguish real writes from writes which will result in a
         * COW page; COW writes should *not* poke the journal (the file will not
         * be changed). Doing so would cause unintended failures when mounted
         * read-only.
         *
         * We check for VM_SHARED rather than vmf->cow_page since the latter is
         * unset for pe_size != PE_SIZE_PTE (i.e. only in do_cow_fault); for
         * other sizes, dax_iomap_fault will handle splitting / fallback so that
         * we eventually come back with a COW page.
         */
        bool write = (vmf->flags & FAULT_FLAG_WRITE) &&
                (vmf->vma->vm_flags & VM_SHARED);
        pfn_t pfn;

        if (write) {
                sb_start_pagefault(sb);
                file_update_time(vmf->vma->vm_file);
                down_read(&EXT4_I(inode)->i_mmap_sem);
retry:
                handle = ext4_journal_start_sb(sb, EXT4_HT_WRITE_PAGE,
                                               EXT4_DATA_TRANS_BLOCKS(sb));
                if (IS_ERR(handle)) {
                        up_read(&EXT4_I(inode)->i_mmap_sem);
                        sb_end_pagefault(sb);
                        return VM_FAULT_SIGBUS;
                }
        } else {
                down_read(&EXT4_I(inode)->i_mmap_sem);
        }
        result = dax_iomap_fault(vmf, pe_size, &pfn, &error, &ext4_iomap_ops);
        if (write) {
                ext4_journal_stop(handle);

                if ((result & VM_FAULT_ERROR) && error == -ENOSPC &&
                    ext4_should_retry_alloc(sb, &retries))
                        goto retry;
                /* Handling synchronous page fault? */
                if (result & VM_FAULT_NEEDDSYNC)
                        result = dax_finish_sync_fault(vmf, pe_size, pfn);
                up_read(&EXT4_I(inode)->i_mmap_sem);
                sb_end_pagefault(sb);
        } else {
                up_read(&EXT4_I(inode)->i_mmap_sem);
        }

        return result;
}

static vm_fault_t ext4_dax_fault(struct vm_fault *vmf)
{
        return ext4_dax_huge_fault(vmf, PE_SIZE_PTE);
}

static const struct vm_operations_struct ext4_dax_vm_ops = {
        .fault          = ext4_dax_fault,
        .huge_fault     = ext4_dax_huge_fault,
        .page_mkwrite   = ext4_dax_fault,
        .pfn_mkwrite    = ext4_dax_fault,
};
#else
#define ext4_dax_vm_ops ext4_file_vm_ops
#endif

static const struct vm_operations_struct ext4_file_vm_ops = {
        .fault          = ext4_filemap_fault,
        .map_pages      = filemap_map_pages,
        .page_mkwrite   = ext4_page_mkwrite,
};

static int ext4_file_mmap(struct file *file, struct vm_area_struct *vma)
{
        struct inode *inode = file->f_mapping->host;
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        struct dax_device *dax_dev = sbi->s_daxdev;

        if (unlikely(ext4_forced_shutdown(sbi)))
                return -EIO;

        /*
         * We don't support synchronous mappings for non-DAX files and
         * for DAX files if underneath dax_device is not synchronous.
         */
        if (!daxdev_mapping_supported(vma, dax_dev))
                return -EOPNOTSUPP;

        file_accessed(file);
        if (IS_DAX(file_inode(file))) {
                vma->vm_ops = &ext4_dax_vm_ops;
                vma->vm_flags |= VM_HUGEPAGE;
        } else {
                vma->vm_ops = &ext4_file_vm_ops;
        }
        return 0;
}

static int ext4_sample_last_mounted(struct super_block *sb,
                                    struct vfsmount *mnt)
{
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        struct path path;
        char buf[64], *cp;
        handle_t *handle;
        int err;

        if (likely(sbi->s_mount_flags & EXT4_MF_MNTDIR_SAMPLED))
                return 0;

        if (sb_rdonly(sb) || !sb_start_intwrite_trylock(sb))
                return 0;

        sbi->s_mount_flags |= EXT4_MF_MNTDIR_SAMPLED;
        /*
         * Sample where the filesystem has been mounted and
         * store it in the superblock for sysadmin convenience
         * when trying to sort through large numbers of block
         * devices or filesystem images.
         */
        memset(buf, 0, sizeof(buf));
        path.mnt = mnt;
        path.dentry = mnt->mnt_root;
        cp = d_path(&path, buf, sizeof(buf));
        err = 0;
        if (IS_ERR(cp))
                goto out;

        handle = ext4_journal_start_sb(sb, EXT4_HT_MISC, 1);
        err = PTR_ERR(handle);
        if (IS_ERR(handle))
                goto out;
        BUFFER_TRACE(sbi->s_sbh, "get_write_access");
        err = ext4_journal_get_write_access(handle, sbi->s_sbh);
        if (err)
                goto out_journal;
        strlcpy(sbi->s_es->s_last_mounted, cp,
                sizeof(sbi->s_es->s_last_mounted));
        ext4_handle_dirty_super(handle, sb);
out_journal:
        ext4_journal_stop(handle);
out:
        sb_end_intwrite(sb);
        return err;
}

static int ext4_file_open(struct inode *inode, struct file *filp)
{
        int ret;

        if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb))))
                return -EIO;

        ret = ext4_sample_last_mounted(inode->i_sb, filp->f_path.mnt);
        if (ret)
                return ret;

        ret = fscrypt_file_open(inode, filp);
        if (ret)
                return ret;

        ret = fsverity_file_open(inode, filp);
        if (ret)
                return ret;

        /*
         * Set up the jbd2_inode if we are opening the inode for
         * writing and the journal is present
         */
        if (filp->f_mode & FMODE_WRITE) {
                ret = ext4_inode_attach_jinode(inode);
                if (ret < 0)
                        return ret;
        }

        filp->f_mode |= FMODE_NOWAIT;
        return dquot_file_open(inode, filp);
}

/*
 * ext4_llseek() handles both block-mapped and extent-mapped maxbytes values
 * by calling generic_file_llseek_size() with the appropriate maxbytes
 * value for each.
 */
loff_t ext4_llseek(struct file *file, loff_t offset, int whence)
{
        struct inode *inode = file->f_mapping->host;
        loff_t maxbytes;

        if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)))
                maxbytes = EXT4_SB(inode->i_sb)->s_bitmap_maxbytes;
        else
                maxbytes = inode->i_sb->s_maxbytes;

        switch (whence) {
        default:
                return generic_file_llseek_size(file, offset, whence,
                                                maxbytes, i_size_read(inode));
        case SEEK_HOLE:
                inode_lock_shared(inode);
                offset = iomap_seek_hole(inode, offset,
                                         &ext4_iomap_report_ops);
                inode_unlock_shared(inode);
                break;
        case SEEK_DATA:
                inode_lock_shared(inode);
                offset = iomap_seek_data(inode, offset,
                                         &ext4_iomap_report_ops);
                inode_unlock_shared(inode);
                break;
        }

        if (offset < 0)
                return offset;
        return vfs_setpos(file, offset, maxbytes);
}

const struct file_operations ext4_file_operations = {
        .llseek         = ext4_llseek,
        .read_iter      = ext4_file_read_iter,
        .write_iter     = ext4_file_write_iter,
        .iopoll         = iomap_dio_iopoll,
        .unlocked_ioctl = ext4_ioctl,
#ifdef CONFIG_COMPAT
        .compat_ioctl   = ext4_compat_ioctl,
#endif
        .mmap           = ext4_file_mmap,
        .mmap_supported_flags = MAP_SYNC,
        .open           = ext4_file_open,
        .release        = ext4_release_file,
        .fsync          = ext4_sync_file,
        .get_unmapped_area = thp_get_unmapped_area,
        .splice_read    = generic_file_splice_read,
        .splice_write   = iter_file_splice_write,
        .fallocate      = ext4_fallocate,
};

const struct inode_operations ext4_file_inode_operations = {
        .setattr        = ext4_setattr,
        .getattr        = ext4_file_getattr,
        .listxattr      = ext4_listxattr,
        .get_acl        = ext4_get_acl,
        .set_acl        = ext4_set_acl,
        .fiemap         = ext4_fiemap,
};