John Garry [Thu, 20 Mar 2025 12:02:50 +0000 (12:02 +0000)]
iomap: rework IOMAP atomic flags
Flag IOMAP_ATOMIC_SW is not really required. The idea of having this flag
is that the FS ->iomap_begin callback could check if this flag is set to
decide whether to do a SW (FS-based) atomic write. But the FS can set
which ->iomap_begin callback it wants when deciding to do a FS-based
atomic write.
Furthermore, it was thought that IOMAP_ATOMIC_HW is not a proper name, as
the block driver can use SW-methods to emulate an atomic write. So change
back to IOMAP_ATOMIC.
The ->iomap_begin callback needs though to indicate to iomap core that
REQ_ATOMIC needs to be set, so add IOMAP_F_ATOMIC_BIO for that.
These changes were suggested by Christoph Hellwig and Dave Chinner.
Gao Xiang [Wed, 19 Mar 2025 08:51:25 +0000 (16:51 +0800)]
iomap: fix inline data on buffered read
Previously, iomap_readpage_iter() returning 0 would break out of the
loops of iomap_readahead_iter(), which is what iomap_read_inline_data()
relies on.
However, commit d9dc477ff6a2 ("iomap: advance the iter directly on
buffered read") changes this behavior without calling
iomap_iter_advance(), which causes EROFS to get stuck in
iomap_readpage_iter().
It seems iomap_iter_advance() cannot be called in
iomap_read_inline_data() because of the iomap_write_begin() path, so
handle this in iomap_readpage_iter() instead.
Reported-and-tested-by: Bo Liu <liubo03@inspur.com> Fixes: d9dc477ff6a2 ("iomap: advance the iter directly on buffered read") Cc: Brian Foster <bfoster@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: "Darrick J. Wong" <djwong@kernel.org> Cc: Christian Brauner <brauner@kernel.org> Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com> Link: https://lore.kernel.org/r/20250319085125.4039368-1-hsiangkao@linux.alibaba.com Reviewed-by: Brian Foster <bfoster@redhat.com> Signed-off-by: Christian Brauner <brauner@kernel.org>
iomap: Lift blocksize restriction on atomic writes
Filesystems like ext4 can submit writes in multiples of blocksizes.
But we still can't allow the writes to be split. Hence let's check if
the iomap_length() is same as iter->len or not.
It is the role of the FS to ensure that a single mapping may be created
for an atomic write. The FS will also continue to check size and alignment
legality.
Signed-off-by: "Ritesh Harjani (IBM)" <ritesh.list@gmail.com>
jpg: Tweak commit message Reviewed-by: "Darrick J. Wong" <djwong@kernel.org> Signed-off-by: John Garry <john.g.garry@oracle.com> Link: https://lore.kernel.org/r/20250303171120.2837067-7-john.g.garry@oracle.com Signed-off-by: Christian Brauner <brauner@kernel.org>
John Garry [Mon, 3 Mar 2025 17:11:13 +0000 (17:11 +0000)]
iomap: Support SW-based atomic writes
Currently atomic write support requires dedicated HW support. This imposes
a restriction on the filesystem that disk blocks need to be aligned and
contiguously mapped to FS blocks to issue atomic writes.
XFS has no method to guarantee FS block alignment for regular,
non-RT files. As such, atomic writes are currently limited to 1x FS block
there.
To deal with the scenario that we are issuing an atomic write over
misaligned or discontiguous data blocks - and raise the atomic write size
limit - support a SW-based software emulated atomic write mode. For XFS,
this SW-based atomic writes would use CoW support to issue emulated untorn
writes.
It is the responsibility of the FS to detect discontiguous atomic writes
and switch to IOMAP_DIO_ATOMIC_SW mode and retry the write. Indeed,
SW-based atomic writes could be used always when the mounted bdev does
not support HW offload, but this strategy is not initially expected to be
used.
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