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BRT: Fix FICLONE/FICLONERANGE shortened copy

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On Linux the ioctl_ficlonerange() and ioctl_ficlone() system calls
are expected to either fully clone the specified range or return an
error.  The range may be for an entire file.  While internally ZFS
supports cloning partial ranges there's no way to return the length
cloned to the caller so we need to make this all or nothing.

As part of this change support for the REMAP_FILE_CAN_SHORTEN flag
has been added.  When REMAP_FILE_CAN_SHORTEN is set zfs_clone_range()
will return a shortened range when encountering pending dirty records.
When it's clear zfs_clone_range() will block and wait for the records
to be written out allowing the blocks to be cloned.

Furthermore, the file range lock is held over the region being cloned
to prevent it from being modified while cloning.  This doesn't quite
provide an atomic semantics since if an error is encountered only a
portion of the range may be cloned.  This will be converted to an
error if REMAP_FILE_CAN_SHORTEN was not provided and returned to the
caller.  However, the destination file range is left in an undefined
state.

A test case has been added which exercises this functionality by
verifying that `cp --reflink=never|auto|always` works correctly.

Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #15728
Closes #15842
This commit is contained in:
Tony Hutter
2024-02-06 09:55:43 -08:00
parent 9ef15845f5
commit 00d85a98ea
13 changed files with 243 additions and 39 deletions
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man/man4/zfs.4
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@@ -1142,6 +1142,15 @@ Enable the experimental block cloning feature.
If this setting is 0, then even if feature@block_cloning is enabled,
attempts to clone blocks will act as though the feature is disabled.
.
.It Sy zfs_bclone_wait_dirty Ns = Ns Sy 0 Ns | Ns 1 Pq int
When set to 1 the FICLONE and FICLONERANGE ioctls wait for dirty data to be
written to disk.
This allows the clone operation to reliably succeed when a file is
modified and then immediately cloned.
For small files this may be slower than making a copy of the file.
Therefore, this setting defaults to 0 which causes a clone operation to
immediately fail when encountering a dirty block.
.
.It Sy zfs_blake3_impl Ns = Ns Sy fastest Pq string
Select a BLAKE3 implementation.
.Pp