OpenAFS Master Repository branch, master, updated. BP-openafs-stable-1_8_x-158-g0322dd5

[Gerrit Code Review]

The following commit has been merged in the master branch:
commit 0322dd56b20b2e2fd6eb7f217964174fb5d25cdd
Author: Andrew Deason <adeason@sinenomine.net>
Date:   Thu Jun 28 13:08:47 2018 -0500

    afs: Change afs_AllocDCache to return error codes
    
    Currently, afs_AllocDCache can fail in 2 different situations:
    
    - When we are out of dslots on the free/discard lists
    - When we encounter an i/o error when trying to traverse the dslot
      lists
    
    But afs_AllocDCache cannot distinguish between these two cases to its
    caller in any way, since all we have to return is a struct dcache (and
    so we return NULL on any error).
    
    Currently, the caller of afs_AllocDCache in afs_GetDCache is
    determining which of these cases happened by looking at
    afs_discardDCList and afs_freeDCList, to see if they look empty. This
    is not great for at least a couple of reasons:
    
    - We are examining afs_discardDCList/afs_freeDCList after we drop
      afs_xdcache (but while still holding GLOCK)
    
    - If afs_discardDCList/afs_freeDCList are somehow changed while
      afs_AllocDCache is running, we may infer the wrong reason why
      afs_AllocDCache failed. (currently impossible, but this seems
      fragile)
    
    And in general, this check against afs_discardDCList/afs_freeDCList is
    rather indirect. It may be easier to follow if afs_AllocDCache just
    directly returned the reason why it failed.
    
    So do that, by changing afs_AllocDCache to return an error code, and
    providing the struct dcache in an output argument. This involves
    similiarly changing several called functions in the same way, to
    return error codes. We only define 2 such error codes with this
    commit:
    
    - ENOSPC, when we are out of free/discrad dslots
    - EIO, when we encounter a disk i/o error when trying to examine the
      dslot list
    
    Note that this commit should not change any real logic; we're mostly
    just changing how errors are returned from these various functions.
    
    Change-Id: I07cc3d7befdcc98360889f4a2ba01fdc9de50848
    Reviewed-on: https://gerrit.openafs.org/13227
    Tested-by: BuildBot <buildbot@rampaginggeek.com>
    Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>

 src/afs/afs_dcache.c |  109 ++++++++++++++++++++++++++++++--------------------
 1 files changed, 65 insertions(+), 44 deletions(-)

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