When an attribute data does not fill then entire remote block, we
zero the remaining part of the buffer. This, however, needs to take
into account that the buffer has a header, and so the offset where
zeroing starts and the length of zeroing need to take this into
account. Otherwise we end up with zeros over the end of the
attribute value when CRCs are enabled.
While there, make sure we only ask to map an extent that covers the
remaining range of the attribute, rather than asking every time for
the full length of remote data. If the remote attribute blocks are
contiguous with other parts of the attribute tree, it will map those
blocks as well and we can potentially zero them incorrectly. We can
also get buffer size mistmatches when trying to read or remove the
remote attribute, and this can lead to not finding the correct
buffer when looking it up in cache.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Ben Myers <bpm@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
Reading a maximally size remote attribute fails when CRCs are
enabled with this verification error:
XFS (vdb): remote attribute header does not match required off/len/owner)
There are two reasons for this, the first being that the
length of the buffer being read is determined from the
args->rmtblkcnt which doesn't take into account CRC headers. Hence
the mapped length ends up being too short and so we need to
calculate it directly from the value length.
The second is that the byte count of valid data within a buffer is
capped by the length of the data and so doesn't take into account
that the buffer might be longer due to headers. Hence we need to
calculate the data space in the buffer first before calculating the
actual byte count of data.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Ben Myers <bpm@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
When CRCs are enabled, there may be multiple allocations made if the
headers cause a length overflow. This, however, does not mean that
the number of headers required increases, as the second and
subsequent extents may be contiguous with the previous extent. Hence
when we map the extents to write the attribute data, we may end up
with less extents than allocations made. Hence the assertion that we
consume the number of headers we calculated in the allocation loop
is incorrect and needs to be removed.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Ben Myers <bpm@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
- optimise the calcuation for the number of blocks in a remote
xattr.
- check attribute length against MAX_XATTR_SIZE, not MAXPATHLEN
- whitespace fixes
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Ben Myers <bpm@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
There are two ways of doing this - the first is to add a CRC to the
remote attribute entry in the attribute block. The second is to
treat them similar to the remote symlink, where each fragment has
it's own header and identifies fragment location in the attribute.
The problem with the CRC in the remote attr entry is that we cannot
identify the owner of the metadata from the metadata blocks
themselves, or where the blocks fit into the remote attribute. The
down side to this approach is that we never know when the attribute
has been read from disk or not and so we have to verify it every
time it is read, and we must calculate it during the create
transaction and log it. We do not log CRCs for any other metadata,
and so this creates a unique set of coherency problems that, in
general, are best avoided.
Adding an identifying header to each allocated block allows us to
identify each fragment and where in the attribute it is located. It
enables us to rebuild the remote attribute from just the raw blocks
containing the attribute. It also provides us to do per-block CRCs
verification at IO time rather than during the transaction context
that creates it or every time it is read into a user buffer. Hence
it avoids all the problems that an external, logged CRC has, and
provides all the benefits of self identifying metadata.
The only complexity is that we have to add a header per fragment,
and we don't know how many fragments will be needed prior to
allocations. If we take the symlink example, the header is 56 bytes
and hence for a 4k block size filesystem, in the worst case 16
headers requires 1 extra block for the 64k attribute data. For 512
byte filesystems the worst case is an extra block for every 9
fragments (i.e. 16 extra blocks in the worse case). This will be
very rare and so it's not really a major concern.
Because allocation is done in two steps - the first finds a hole
large enough in the attribute file, the second does the allocation -
we only need to find a hole big enough for a worst case allocation.
We only need to allocate enough extra blocks for number of headers
required by the fragments, and we can calculate that as we go....
Hence it really only makes sense to use the same model as for
symlinks - it doesn't add that much complexity, does not require an
attribute tree format change, and does not require logging
calculated CRC values.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Ben Myers <bpm@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
Adding CRC support to remote attributes adds a significant amount of
remote attribute specific code. Split the existing remote attribute
code out into it's own file so that all the relevant remote
attribute code is in a single, easy to find place.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Ben Myers <bpm@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
