[Gluster-devel] glfs_readdir_r is painful

[Anand Avati]

Eric,
Thanks for the insights. I have posted a patch at
http://review.gluster.org/6201 which clarifies the usage of
glfs_readdir_r() and also introduce glfs_readdir().

Thanks,
Avati


On Wed, Oct 30, 2013 at 11:05 AM, Eric Blake <eblake at redhat.com> wrote:

> On 10/30/2013 11:18 AM, Eric Blake wrote:
>
> > The only safe way to use readdir_r is to know the maximum d_name that
> > can possibly be returned, but there is no glfs_fpathconf() for
> > determining that information.  Your example usage of glfs_readdir_r()
> > suggests that 512 bytes is large enough:
> >
> https://forge.gluster.org/glusterfs-core/glusterfs/blobs/f44ada6cd9bcc5ab98ca66bedde4fe23dd1c3f05/api/examples/glfsxmp.c
> > but I don't know if that is true.
>
> Okay, after a bit more investigation, I see:
>
> gf_dirent_to_dirent (gf_dirent_t *gf_dirent, struct dirent *dirent)
> {
>         dirent->d_ino = gf_dirent->d_ino;
>
> #ifdef _DIRENT_HAVE_D_OFF
>         dirent->d_off = gf_dirent->d_off;
> #endif
>
> #ifdef _DIRENT_HAVE_D_TYPE
>         dirent->d_type = gf_dirent->d_type;
> #endif
>
> #ifdef _DIRENT_HAVE_D_NAMLEN
>         dirent->d_namlen = strlen (gf_dirent->d_name);
> #endif
>
>         strncpy (dirent->d_name, gf_dirent->d_name, 256);
> }
>
> I also discovered that 'getconf NAME_MAX /path/to/xfs/mount' is 255, so
> it looks like you got lucky (although strncpy is generally unsafe
> because it fails to write a NUL terminator if you truncate the string,
> it looks like you are guaranteed by XFS to never have a string that
> needs truncation).
>
> >  You _do_ have the advantage that
> > since every brick backing a glusterfs volume is using an xfs file
> > system, then you only have to worry about the NAME_MAX of xfs - but I
> > don't know that value off the top of my head.
>
> Again, my research shows it is 255.
>
> >  Can you please let me
> > know how big I should make my struct dirent to avoid buffer overflow,
> > and properly document this in <glusterfs/api/glfs.h>?  Furthermore, can
> > you please provide a much saner glfs_readdir() so I don't have to worry
> > about contortions of using a broken-by-design function?
>
> These requests are still in force.
>
> --
> Eric Blake   eblake redhat com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
>
>
> _______________________________________________
> Gluster-devel mailing list
> Gluster-devel at nongnu.org
> https://lists.nongnu.org/mailman/listinfo/gluster-devel
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://supercolony.gluster.org/pipermail/gluster-devel/attachments/20131030/ae7afbfb/attachment-0001.html>