[PATCH 0/3 V1] cifs: cache the directory content for shroot

[Ronnie Sahlberg <lsahlber@redhat.com>]

Steve, Aurelien, List

Please find updated version.
With these patches we now server readdir() out of cache for shroot
which eliminates at least three roundtrips:
* the initial Create+QueryDirectory
* the Query_Directory that fails with no more files
* the Close

Since we only cache name, inode and type we will still have the 
Create/GetInfo/Close calls for every direcotry member.
To solve that and eliminate those calls I chatted with Steve
and we could cache all information about those child objects for ~1 second.

That would not plug into cifs_readdir() but in parts different parts of
the cifs.ko code so it should into its own patch for
"fetch stat() data for objects from the directory cache, if available".
That would be a different patch series.


V3:
* always take out shroot on the master tcon
* fix bug where we would still do one FindFirst even if we had everything cached

V2: addressing Aureliens comments
* Fix comment style
* Describe what ctx->pos == 2 means
* use is_smb1_server()


See initial implementation of a mechanism to cache the directory entries for
a shared cache handle (shroot).
We cache all the entries during the initial readdir() scan, using the context
from the vfs layer as the key to handle if there are multiple concurrent readir() scans
of the same directory.
Then if/when we have successfully cached the entire direcotry we will server any
subsequent readdir() from out of cache, avoinding making any query direcotry calls to the server.

As with all of shroot, the cache is kept until the direcotry lease is broken.


The first two patches are small and just a preparation for the third patch. They go as separate
patches to make review easier.
The third patch adds the actual meat of the dirent caching .


For now this might not be too exciting because the only cache the root handle.
I hope in the future we will expand the directory caching to handle any/many direcotries.