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I noticed a bug in ranged GETFSMAP queries:
# xfs_io -c 'fsmap -vvvv' /opt
EXT: DEV BLOCK-RANGE OWNER FILE-OFFSET AG AG-OFFSET TOTAL
0: 8:80 [0..7]: static fs metadata 0 (0..7) 8
<snip>
9: 8:80 [192..223]: 137 0..31 0 (192..223) 32
# xfs_io -c 'fsmap -vvvv -d 208 208' /opt
#
That's not right -- we asked what block maps block 208, and we should've
received a mapping for inode 137 offset 16. Instead, we get nothing.
The root cause of this problem is a mis-interaction between the fsmap
code and how btree ranged queries work. xfs_btree_query_range returns
any btree record that overlaps with the query interval, even if the
record starts before or ends after the interval. Similarly, GETFSMAP is
supposed to return a recordset containing all records that overlap the
range queried.
However, it's possible that the recordset is larger than the buffer that
the caller provided to convey mappings to userspace. In /that/ case,
userspace is supposed to copy the last record returned to fmh_keys[0]
and call GETFSMAP again. In this case, we do not want to return
mappings that we have already supplied to the caller. The call to
xfs_btree_query_range is the same, but now we ignore any records that
start before fmh_keys[0].
Unfortunately, we didn't implement the filtering predicate correctly.
The predicate should only be called when we're calling back for more
records. Accomplish this by setting info->low.rm_blockcount to a
nonzero value and ensuring that it is cleared as necessary. As a
result, we no longer want to adjust dkeys[0] in the main setup function
because that's confusing.
This patch doesn't touch the logdev/rtbitmap backends because they have
bigger problems that will be addressed by subsequent patches.
Found via xfs/556 with parent pointers enabled.
Fixes: e89c041338 ("xfs: implement the GETFSMAP ioctl")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.