cvs commit: src/sys/ufs/ufs ufs_lookup.c

[Brian Fundakowski Feldman]

On Wed, Mar 08, 2006 at 11:24:22AM -0600, Eric Anderson wrote:
> Ruslan Ermilov wrote:
> >On Wed, Mar 08, 2006 at 03:16:25AM -0500, Kris Kennaway wrote:
> >  
> >>On Wed, Mar 08, 2006 at 09:06:32AM +0200, Ruslan Ermilov wrote:
> >>    
> >>>On Wed, Mar 08, 2006 at 02:14:39AM +0000, Tor Egge wrote:
> >>>      
> >>>>tegge       2006-03-08 02:14:39 UTC
> >>>>
> >>>>  FreeBSD src repository
> >>>>
> >>>>  Modified files:
> >>>>    sys/ufs/ufs          ufs_lookup.c 
> >>>>  Log:
> >>>>  Don't set IN_CHANGE and IN_UPDATE on inodes for potentially suspended
> >>>>  file systems.  This could cause deadlocks when creating snapshots.
> >>>>  
> >>>>  Reviewed by:    jeff
> >>>>  
> >>>>  Revision  Changes    Path
> >>>>  1.80      +0 -1      src/sys/ufs/ufs/ufs_lookup.c
> >>>>
> >>>>        
> >>>Like for example "ls -l /filesystem/.snap" when "fsck -B" is in place?
> >>>      
> >>Is that a deadlock, or just the process being suspended until fsck
> >>finishes?
> >>    
> 
> I think the only options we have to fix this is to either make the .snap
> directory 'hidden' (which is not a feature yet), or to possibly cache
> the inode information on parent directories containing snapshots, so
> when a fs is suspended or a snapshot is in progress, a stat of the
> parent directory of the snapshots' doesn't block until the snapshot
> finishes.
> 
> There has been brief discussion on freebsd-fs@ about adding a 'hidden'
> flag (usable with chflags) to files and directories, and tools like ls,
> etc, that would normally stat each file/dir in a directory would ignore,
> unless a special option was used.  That would not stop other tools doing
> stat calls from seeing it though, but I think most of the blocking
> happens when a user does an ls -al in the directory.

That's the same reason I don't mount random stuff onto the root
directory.  Everything that walks the filesystem can block way too
easily (and inadvertently), and using /disk (or a convention like
OS X's /Volumes) circumvents most of these problems.  Having one
per-mount is a little ugly, but /mnt/.metadata/snapshots isn't
really THAT much worse.

-- 
Brian Fundakowski Feldman                           \'[ FreeBSD ]''''''''''\
  <> green at FreeBSD.org                               \  The Power to Serve! \
 Opinions expressed are my own.                       \,,,,,,,,,,,,,,,,,,,,,,\