git: hammer2 kernel: mfs -- Fix unmount panic for MFS filesystems.

[Venkatesh Srinivas <vsrinivas@xxxxxxxxxxxxxxxxxxxxxxx>]

commit f39f7550bfabac2d1290b91a0e5c6c37d276bca7
Author: Venkatesh Srinivas <me@endeavour.zapto.org>
Date:   Thu Feb 16 07:53:22 2012 -0800

    kernel: mfs -- Fix unmount panic for MFS filesystems.
    
    mfs_start() is active for the life of an MFS mount, handling copyin/out
    requests. It is directed to exit when an MFS filesystem is unmounted.
    The VFS accounting code and VFS MPLOCK code assumed that the mountpoint
    structure was stable on return of mfs_start, which was not the case.
    
    To work around that, don't call acinit if the vfs_start vfsop returns
    EMOUNTEXIT, a kernel-specific pseudo-errno. Also allow marking vfs_start
    MPSAFE and mark mfs vfs_start MPSAFE, to avoid accessing a per-mount
    token field. A future commit will rework MFS's locking so that critical
    sections are not used to protect the MFS bioq.
    
    This is a hack for MFS; future work should either rework the filesystem
    or replace it outright with tmpfs.
    
    Closes: Bug 2276

Summary of changes:
 sys/kern/vfs_vfsops.c    |    4 +++-
 sys/sys/errno.h          |    1 +
 sys/sys/mount.h          |    4 +++-
 sys/vfs/mfs/mfs_vfsops.c |    8 +++++++-
 4 files changed, 14 insertions(+), 3 deletions(-)

http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/f39f7550bfabac2d1290b91a0e5c6c37d276bca7


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