From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jonathan Loran Subject: Re: statfs() and autofs Date: Tue, 15 Jul 2008 22:21:31 -0700 Message-ID: <487D855B.8000405@loran.name> References: <20080715204839.GU5858@pixar.com> <1216179794.22783.46.camel@raven.themaw.net> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============5564912433753830772==" Return-path: In-Reply-To: <1216179794.22783.46.camel@raven.themaw.net> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: autofs-bounces@linux.kernel.org Errors-To: autofs-bounces@linux.kernel.org To: Ian Kent Cc: autofs@linux.kernel.org This is a multi-part message in MIME format. --===============5564912433753830772== Content-Type: multipart/alternative; boundary="------------070304010803090202070509" This is a multi-part message in MIME format. --------------070304010803090202070509 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Ian Kent wrote: > On Tue, 2008-07-15 at 13:48 -0700, Chris Walker wrote: > >> autofs 5.0.3 >> linux 2.6.18 >> >> When statfs() is called on an automounted directory, it returns before >> the automount occurs. This results in output like this initially: >> > > That may be because there are a group of system calls that don't trigger > a mount because we have to avoid mount storms for map entries that use > the browse option. In particular stat(2) and calls that use the same > kernel path lookup flags, such as statfs(2). > > Basically, if the mount point directory exists in the autofs file system > but doesn't currently have a mount for some reason (perhaps it wasn't > removed at expire or the entry uses the browse option), these calls will > return the attributes of the autofs directory without performing a > mount. > > Hi Ian, I need to say that this basically has to be declared a bug. I have been silent on this until now because I am so over committed with other tasks, and haven't had time to test it so cleanly as Chris has. At my lab we find that on machines that do large batch processing, automounted directories often aren't there at the time that they are stat-ed. The workaround has been to put in some nanosleeps to give the mount point a chance to mount, but that is very much a hack, since now the code authors need to know the point where an automount is joined, or they at least have to find it out empirically. The code they write has become unportable and for all we know, incompatible on other systems if the autofs mount points are different. To throw this in the mix, somehow, our Solaris systems, which share identical automount maps, simply never have this issue. Is there an architectural reason for this? And if so, can we learn how this is so, and apply similar logic to the Linux autofs/mount path? Thanks, Jon --------------070304010803090202070509 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit

Ian Kent wrote: 
On Tue, 2008-07-15 at 13:48 -0700, Chris Walker wrote:
  
autofs 5.0.3
linux 2.6.18

When statfs() is called on an automounted directory, it returns before
the automount occurs. This results in output like this initially:
    

That may be because there are a group of system calls that don't trigger
a mount because we have to avoid mount storms for map entries that use
the browse option. In particular stat(2) and calls that use the same
kernel path lookup flags, such as statfs(2).

Basically, if the mount point directory exists in the autofs file system
but doesn't currently have a mount for some reason (perhaps it wasn't
removed at expire or the entry uses the browse option), these calls will
return the attributes of the autofs directory without performing a
mount.
Hi Ian,

I need to say that this basically has to be declared a bug.  I have been silent on this until now because I am so over committed with other tasks, and haven't had time to test it so cleanly as Chris has.

At my lab we find that on machines that do large batch processing, automounted directories often aren't there at the time that they are stat-ed.  The workaround has been to put in some nanosleeps to give the mount point a chance to mount, but that is very much a hack, since now the code authors need to know the point where an automount is joined, or they at least have to find it out empirically.  The code they write has become unportable and for all we know, incompatible on other systems if the autofs mount points are different. 

To throw this in the mix, somehow, our Solaris systems, which share identical automount maps, simply never have this issue.  Is there an architectural reason for this?  And if so, can we learn how this is so, and apply similar logic to the Linux autofs/mount path?

Thanks,

Jon
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