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    Subject[PATCH v4 6/9] iomap: don't increase i_size if it's not a write operation
    Date
    From: Zhang Yi <yi.zhang@huawei.com>

    Increase i_size in iomap_zero_range() and iomap_unshare_iter() is not
    needed, the caller should handle it. Especially, when truncate partial
    block, we should not increase i_size beyond the new EOF here. It doesn't
    affect xfs and gfs2 now because they set the new file size after zero
    out, it doesn't matter that a transient increase in i_size, but it will
    affect ext4 because it set file size before truncate. So move the i_size
    updating logic to iomap_write_iter().

    Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
    Reviewed-by: Christoph Hellwig <hch@lst.de>
    Reviewed-by: Darrick J. Wong <djwong@kernel.org>
    ---
    fs/iomap/buffered-io.c | 50 +++++++++++++++++++++---------------------
    1 file changed, 25 insertions(+), 25 deletions(-)

    diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
    index 7e32a204650b..e9112dc78d15 100644
    --- a/fs/iomap/buffered-io.c
    +++ b/fs/iomap/buffered-io.c
    @@ -837,32 +837,13 @@ static size_t iomap_write_end(struct iomap_iter *iter, loff_t pos, size_t len,
    size_t copied, struct folio *folio)
    {
    const struct iomap *srcmap = iomap_iter_srcmap(iter);
    - loff_t old_size = iter->inode->i_size;
    - size_t ret;
    -
    - if (srcmap->type == IOMAP_INLINE) {
    - ret = iomap_write_end_inline(iter, folio, pos, copied);
    - } else if (srcmap->flags & IOMAP_F_BUFFER_HEAD) {
    - ret = block_write_end(NULL, iter->inode->i_mapping, pos, len,
    - copied, &folio->page, NULL);
    - } else {
    - ret = __iomap_write_end(iter->inode, pos, len, copied, folio);
    - }
    -
    - /*
    - * Update the in-memory inode size after copying the data into the page
    - * cache. It's up to the file system to write the updated size to disk,
    - * preferably after I/O completion so that no stale data is exposed.
    - */
    - if (pos + ret > old_size) {
    - i_size_write(iter->inode, pos + ret);
    - iter->iomap.flags |= IOMAP_F_SIZE_CHANGED;
    - }
    - __iomap_put_folio(iter, pos, ret, folio);

    - if (old_size < pos)
    - pagecache_isize_extended(iter->inode, old_size, pos);
    - return ret;
    + if (srcmap->type == IOMAP_INLINE)
    + return iomap_write_end_inline(iter, folio, pos, copied);
    + if (srcmap->flags & IOMAP_F_BUFFER_HEAD)
    + return block_write_end(NULL, iter->inode->i_mapping, pos, len,
    + copied, &folio->page, NULL);
    + return __iomap_write_end(iter->inode, pos, len, copied, folio);
    }

    static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
    @@ -877,6 +858,7 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)

    do {
    struct folio *folio;
    + loff_t old_size;
    size_t offset; /* Offset into folio */
    size_t bytes; /* Bytes to write to folio */
    size_t copied; /* Bytes copied from user */
    @@ -926,6 +908,22 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
    copied = copy_folio_from_iter_atomic(folio, offset, bytes, i);
    status = iomap_write_end(iter, pos, bytes, copied, folio);

    + /*
    + * Update the in-memory inode size after copying the data into
    + * the page cache. It's up to the file system to write the
    + * updated size to disk, preferably after I/O completion so that
    + * no stale data is exposed. Only once that's done can we
    + * unlock and release the folio.
    + */
    + old_size = iter->inode->i_size;
    + if (pos + status > old_size) {
    + i_size_write(iter->inode, pos + status);
    + iter->iomap.flags |= IOMAP_F_SIZE_CHANGED;
    + }
    + __iomap_put_folio(iter, pos, status, folio);
    +
    + if (old_size < pos)
    + pagecache_isize_extended(iter->inode, old_size, pos);
    if (status < bytes)
    iomap_write_failed(iter->inode, pos + status,
    bytes - status);
    @@ -1298,6 +1296,7 @@ static loff_t iomap_unshare_iter(struct iomap_iter *iter)
    bytes = folio_size(folio) - offset;

    bytes = iomap_write_end(iter, pos, bytes, bytes, folio);
    + __iomap_put_folio(iter, pos, bytes, folio);
    if (WARN_ON_ONCE(bytes == 0))
    return -EIO;

    @@ -1362,6 +1361,7 @@ static loff_t iomap_zero_iter(struct iomap_iter *iter, bool *did_zero)
    folio_mark_accessed(folio);

    bytes = iomap_write_end(iter, pos, bytes, bytes, folio);
    + __iomap_put_folio(iter, pos, bytes, folio);
    if (WARN_ON_ONCE(bytes == 0))
    return -EIO;

    --
    2.39.2

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