The zero range operation is analogous to fallocate with the exception of converting the range to zeroes. E.g., it attempts to allocate zeroed blocks over the range specified by the caller. The XFS implementation kills all delalloc blocks currently over the aligned range, converts the range to allocated zero blocks (unwritten extents) and handles the partial pages at the ends of the range by sending writes through the pagecache. The current implementation suffers from several problems associated with inode size. If the aligned range covers an extending I/O, said I/O is discarded and an inode size update from a previous write never makes it to disk. Further, if an unaligned zero range extends beyond eof, the page write induced for the partial end page can itself increase the inode size, even if the zero range request is not supposed to update i_size (via KEEP_SIZE, similar to an fallocate beyond EOF). The latter behavior not only incorrectly increases the inode size, but can lead to stray delalloc blocks on the inode. Typically, post-eof preallocation blocks are either truncated on release or inode eviction or explicitly written to by xfs_zero_eof() on natural file size extension. If the inode size increases due to zero range, however, associated blocks leak into the address space having never been converted or mapped to pagecache pages. A direct I/O to such an uncovered range cannot convert the extent via writeback and will BUG(). For example: $ xfs_io -fc "pwrite 0 128k" -c "fzero -k 1m 54321" <file> ... $ xfs_io -d -c "pread 128k 128k" <file> <BUG> If the entire delalloc extent happens to not have page coverage whatsoever (e.g., delalloc conversion couldn't find a large enough free space extent), even a full file writeback won't convert what's left of the extent and we'll assert on inode eviction. Rework xfs_zero_file_space() to avoid buffered I/O for partial pages. Use the existing hole punch and prealloc mechanisms as primitives for zero range. This implementation is not efficient nor ideal as we writeback dirty data over the range and remove existing extents rather than convert to unwrittern. The former writeback, however, is currently the only mechanism available to ensure consistency between pagecache and extent state. Even a pagecache truncate/delalloc punch prior to hole punch has lead to inconsistencies due to racing with writeback. This provides a consistent, correct implementation of zero range that survives fsstress/fsx testing without assert failures. The implementation can be optimized from this point forward once the fundamental issue of pagecache and delalloc extent state consistency is addressed. Signed-off-by: Brian Foster <bfoster@redhat.com> Reviewed-by: Dave Chinner <dchinner@redhat.com> Signed-off-by: Dave Chinner <david@fromorbit.com>
XFS currently discards delalloc blocks within the target range of a zero range request. Unaligned start and end offsets are zeroed through the page cache and the internal, aligned blocks are converted to unwritten extents. If EOF is page aligned and covered by a delayed allocation extent. The inode size is not updated until I/O completion. If a zero range request discards a delalloc range that covers page aligned EOF as such, the inode size update never occurs. For example: $ rm -f /mnt/file $ xfs_io -fc "pwrite 0 64k" -c "zero 60k 4k" /mnt/file $ stat -c "%s" /mnt/file 65536 $ umount /mnt $ mount <dev> /mnt $ stat -c "%s" /mnt/file 61440 Update xfs_zero_file_space() to flush the range rather than discard delalloc blocks to ensure that inode size updates occur appropriately. [dchinner: Note that this is really a workaround to avoid the underlying problems. More work is needed (and ongoing) to fix those issues so this fix is being added as a temporary stop-gap measure. ] Signed-off-by: Brian Foster <bfoster@redhat.com> Reviewed-by: Dave Chinner <dchinner@redhat.com> Signed-off-by: Dave Chinner <david@fromorbit.com>
xfs_zero_remaining_bytes() open codes a log of buffer manupulations to do a read forllowed by a write. It can simply be replaced by an uncached read followed by a xfs_bwrite() call. Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Dave Chinner <dchinner@redhat.com> Signed-off-by: Dave Chinner <david@fromorbit.com>
There is a lot of cookie-cutter code that looks like: if (shutdown) handle buffer error xfs_buf_iorequest(bp) error = xfs_buf_iowait(bp) if (error) handle buffer error spread through XFS. There's significant complexity now in xfs_buf_iorequest() to specifically handle this sort of synchronous IO pattern, but there's all sorts of nasty surprises in different error handling code dependent on who owns the buffer references and the locks. Pull this pattern into a single helper, where we can hide all the synchronous IO warts and hence make the error handling for all the callers much saner. This removes the need for a special extra reference to protect IO completion processing, as we can now hold a single reference across dispatch and waiting, simplifying the sync IO smeantics and error handling. In doing this, also rename xfs_buf_iorequest to xfs_buf_submit and make it explicitly handle on asynchronous IO. This forces all users to be switched specifically to one interface or the other and removes any ambiguity between how the interfaces are to be used. It also means that xfs_buf_iowait() goes away. Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Dave Chinner <david@fromorbit.com>
Fix sparse warning introduced by commit 4ef897a ("xfs: flush both
inodes in xfs_swap_extents").
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>
xfs_free_file_space() only affects the range of the file for which space is being freed. It currently writes and truncates the page cache from the start offset of the free to EOF. Modify xfs_free_file_space() to write back and truncate page cache of just the range being freed. Signed-off-by: Brian Foster <bfoster@redhat.com> Reviewed-by: Dave Chinner <dchinner@redhat.com> Signed-off-by: Dave Chinner <david@fromorbit.com>
The collapse range operation currently writes the entire file before starting the collapse to avoid changes in the in-core extent list due to writeback causing the extent count to change. Now that collapse range is fsb based rather than extent index based it can sustain changes in the extent list during the shift sequence without disruption. Modify xfs_collapse_file_space() to writeback and invalidate pages associated with the range of the file to be shifted. xfs_free_file_space() currently has similar behavior, but the space free need only affect the region of the file that is freed and this could change in the future. Also update the comments to reflect the current implementation. We retain the eofblocks trim permanently as a best option for dealing with delalloc extents. We don't shift delalloc extents because this scenario only occurs with post-eof preallocation (since data must be flushed such that the cache can be invalidated and data can be shifted). That means said space must also be initialized before being shifted into the accessible region of the file only to be immediately truncated off as the last part of the collapse. In other words, the eofblocks trim will happen anyways, we just run it first to ensure the file remains in a consistent state throughout the collapse. Finally, detect and fail explicitly in the event of a delalloc extent during the extent shift. The implementation does not support delalloc extents and the caller is expected to prevent this scenario in advance as is done by collapse. Signed-off-by: Brian Foster <bfoster@redhat.com> Reviewed-by: Dave Chinner <dchinner@redhat.com> Signed-off-by: Dave Chinner <david@fromorbit.com>