The intent of this new field in the directory entry is to
allow a subsequent lookup to know how many blocks, which
are contiguous with the inode, contain metadata which relates
to the inode. This will then allow the issuing of a single
read to read these blocks, rather than reading the inode
first, and then issuing a second read for the metadata.
This only works under some fairly strict conditions, since
we do not have back pointers from inodes to directory entries
we must ensure that the blocks referenced in this way will
always belong to the inode.
This rules out being able to use this system for indirect
blocks, as these can change as a result of truncate/rewrite.
So the idea here is to restrict this to xattr blocks only
for the time being. For most inodes, that means only a
single block. Also, when using ACLs and/or SELinux or
other LSMs, these will be added at inode creation time
so that they will be contiguous with the inode on disk and
also will almost always be needed when we read the inode in
for permissions checks.
Once an xattr block for an inode is allocated, it will never
change until the inode is deallocated.
This patch adds the new field, a further patch will add the
readahead in due course.
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
This is another step towards improving the allocation of xattr
blocks at inode allocation time. Here we take advantage of
Christoph's recent work on ACLs to allocate a block for the
xattrs early if we know that we will be adding ACLs to the
inode later on. The advantage of that is that it is much
more likely that we'll get a contiguous run of two blocks
where the first is the inode and the second is the xattr block.
We still have to fall back to the original system in case we
don't get the requested two contiguous blocks, or in case the
ACLs are too large to fit into the block.
Future patches will move more of the ACL setting code further
up the gfs2_inode_create() function. Also, I'd like to be
able to do the same thing with the xattrs from LSMs in
due course, too. That way we should be able to slowly reduce
the number of independent transactions, at least in the
most common cases.
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
This patch adds four new fields to directory leaf blocks.
The intent is not to use them in the kernel itself, although
perhaps we may be able to use them as hints at some later date,
but instead to provide more information for debug/fsck use.
One new field adds a pointer to the inode to which the leaf
belongs. This can be useful if the pointer to the leaf block
has become corrupt, as it will allow us to know which inode
this block should be associated with. This field is set when
the leaf is created and never changed over its lifetime.
The second field is a "distance from the hash table" field.
The meaning is as follows:
0 = An old leaf in which this value has not been set
1 = This leaf is pointed to directly from the hash table
2+ = This leaf is part of a chain, pointed to by another leaf
block, the value gives the position in the chain.
The third and fourth fields combine to give a time stamp of
the most recent directory insertion or deletion from this
leaf block. The time stamp is not updated when a new leaf
block is chained from the current one. The code is currently
written such that the timestamp on the dir inode will match
that of the leaf block for the most recent insertion/deletion.
For backwards compatibility, any of these new fields which is
zero should be considered to be "unknown".
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Michael Kerrisk <mtk.manpages@gmail.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Dave Jones <davej@redhat.com>
Steven Whitehouse