[Pvfs2-developers] ACL/getxattr overhead in ls

[Murali Vilayannur]

Hi Rob,

> Yes, it seems reasonable to just tell the kernel that they aren't there
> in the case that ACLs are disabled. However, this might lead to a weird
> situation if a user then decides to play with or set these values. Is it
> possible for a user to adjust ACLs even if the file system mount isn't
> currently honoring them?

Nope. EOPNOTSUPP should be returned if we try to setfacl if mount does not
have -o acl option.

> Just another example of how ls is the worst app ever for file systems.

Couldn't agree with you more :)
Murali

>
> Rob
>
> Phil Carns wrote:
> > We have noticed on RedHat RHEL3 and RHEL4 that when you do a long
> > listing of a directory (on any file system, not just pvfs2) that the ls
> > triggers a getxattr of "system.posix_acl_access" and
> > "system.posix_acl_default" for every single entry that is listed.  This
> > happens regardless of whether ACLs are enabled for the file system or not.
> >
> > Digging in the coreutils/ls source, it turns out that ls (with -l
> > options at least) is checking to see if any acl's are set on each entry
> > so that it can display them differently, maybe with a "+" character.
> >
> > On RHEL3 at least (2.4 kernel) these extra getxattrs are causing 2
> > serialized getxattr requests that are probably significantly slowing
> > down the listing, which is a shame because the 2.4 kernel module doesn't
> > even support ACLs so there is never any point in checking.
> >
> > Does it seem reasonable to add a test in the kernel module so that if a)
> > acl's are not enabled (which can be determined by checking the super
> > block acl flag), and b) the getxattr name matches "system.posix_acl"
> > then we just immediately return an appropriate error code rather than
> > servicing the getxattr?
> >
> > The stock coreutils package doesn't currently have this problem, because
> > their acl check is broken for Linux.  RedHat supplies a patch with their
> > rpm that adds acl checks that work on linux (using the
> > acl_extended_file() function rather than the unsupported acl()
> > function).  I imagine there are other distributions that have done
> > likewise, and probably it will be "fixed" in the official gnu version
> > eventually also.
> >
> > -Phil
> >
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