Re: [PATCH v2 0/3] block: use pwrite_zeroes_alignment when writing first sector

[Kevin Wolf <kwolf@redhat.com>]

Am 07.10.2025 um 16:16 hat Stefan Hajnoczi geschrieben:
> v2:
> - Simplify condition to if (!s->needs_alignment) in patch 1 [Vladimir]
> 
> This series fixes a bug I introduced in commit 5634622bcb33 ("file-posix: allow
> BLKZEROOUT with -t writeback"). The Linux fallocate(2) and ioctl(BLKZEROOUT)
> syscalls require logical block size alignment of the offset and length, even
> when the file is opened in buffered I/O mode where read/write operations do not
> require alignment.
> 
> The fix is to populate the pwrite_zeroes_alignment block limits field and to
> use that limit in create_file_fallback_zero_first_sector().
> 
> One issue I want to raise is that pwrite_zeroes_alignment is an "optimal
> alignment" hint. Hence create_file_fallback_zero_first_sector() had to be
> modified to honor the limit explicitly. The block layer doesn't automatically
> apply padding in order to align requests. This is different from how QEMU's
> block layer pwrite/pread works, where it does automatically apply padding and
> read/modify/write as necessary. If you want consistency, please let me know.

Thanks, applied to the block branch.

Kevin