Re: [PATCH 2/3] xfs: create symlink proc/fs/xfs/stat to sys/fs/xfs/stats

["Bill O'Donnell" <billodo@redhat.com>]

On Thu, Sep 03, 2015 at 01:39:53PM -0500, Bill O'Donnell wrote:
> On Thu, Sep 03, 2015 at 01:32:25PM -0500, Eric Sandeen wrote:
> > On 9/3/15 12:57 PM, Darrick J. Wong wrote:
> > > On Thu, Sep 03, 2015 at 11:36:26AM -0500, billodo wrote:
> > >> As a part of the work to move xfs global stats from procfs to sysfs,
> > >> this patch creates the symlink from proc/fs/xfs/stat to sys/fs/xfs/stats.
> > >>
> > >> Signed-off-by: Bill O'Donnell <billodo@redhat.com>
> > >> ---
> > >>  fs/xfs/xfs_stats.c | 8 ++++++--
> > >>  1 file changed, 6 insertions(+), 2 deletions(-)
> > >>
> > >> diff --git a/fs/xfs/xfs_stats.c b/fs/xfs/xfs_stats.c
> > >> index 856cf57..ad435f1 100644
> > >> --- a/fs/xfs/xfs_stats.c
> > >> +++ b/fs/xfs/xfs_stats.c
> > >> @@ -244,9 +244,13 @@ xfs_init_procfs(void)
> > >>  	if (!proc_mkdir("fs/xfs", NULL))
> > >>  		goto out;
> > >>  
> > >> -	if (!proc_create("fs/xfs/stat", 0, NULL,
> > >> -			 &xfs_stat_proc_fops))
> > >> +	if (!proc_symlink("fs/xfs/stat", NULL,
> > >> +			  "/sys/fs/xfs/stats/stats"))
> > > 
> > > Uh.... is it actually guaranteed that sysfs is mounted on /sys now?
> > > 
> > > I sort of recall gregkh grumbling years ago that sysfs can be mounted anywhere,
> > > and that /proc shouldn't hardcode links to it.  But that's just handwaving on
> > > my part.
> > 
> > You can blame me for that idea.  At least one other driver does
> > do it, though; of_core_init():
> > 
> > proc_symlink("device-tree", NULL, "/sys/firmware/devicetree/base");
> > 
> > worst-case scenario, your "legacy" stats file will be a broken symlink...
> > 
> > -Eric
> > 
> 
> I'm still looking for something in documentation that dictates such a requirement
> regarding symlinks to sysfs elements.
> -Bill

I did find this in: https://www.kernel.org/doc/Documentation/sysfs-rules.txt
--------------snip--------------------------
- sysfs is always at /sys
  Parsing /proc/mounts is a waste of time. Other mount points are a
  system configuration bug you should not try to solve. For test cases,
  possibly support a SYSFS_PATH environment variable to overwrite the
  application's behavior, but never try to search for sysfs. Never try
  to mount it, if you are not an early boot script.
-------------snip---------------------------
> 
> > > --D
> > > 
> > >> +	{
> > >> +		printk(KERN_INFO "failed to created fs/xfs/stat symlink\n");
> > >>  		goto out_remove_xfs_dir;
> > >> +	}
> > >> +
> > >>  #ifdef CONFIG_XFS_QUOTA
> > >>  	if (!proc_create("fs/xfs/xqmstat", 0, NULL,
> > >>  			 &xqmstat_proc_fops))
> > >> -- 
> > >> 2.4.3
> > 
> 
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