Re: [rfc] new stat*fs-like syscall?

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Thu, Jun 24, 2010 at 04:03:05PM +0200, Miklos Szeredi wrote:
> On Thu, 24 Jun 2010, Nick Piggin wrote:
> > This has come up a few times in the past, and I'd like to try to get
> > an agreement on it. statvfs(2) importantly contains f_flag (mount
> > flags), and is encouraged to use rather than statfs(2). The kernel
> > provides a statfs syscall only.
> > 
> > This means glibc has to provide f_flag support by parsing /proc/mounts
> > and stat(2)ing mount points. This is really slow, and /proc/mounts is
> > hard for the kernel to provide. It's actually the last scalability
> > bottleneck in the core vfs for dbench (samba) after my patches.
> > 
> > Not only that, but it's racy.
> > 
> > Other than types, other differences are:
> > - statvfs(2) has is f_frsize, which seems fairly useless.
> 
> statfs(2) also has f_frsize since 2.6.0, only it hasn't been
> documented (should be fixed now).
> 
> > - statvfs(2) has f_favail.
> > - statfs(2) f_bsize is optimal transfer block, statvfs(2) f_bsize is fs
> >   block size. The latter could be useful for disk space algorithms.
> >   Both can be ill defned.
> 
> They are the same, only the documentation is different.
> 
> > - statvfs(2) lacks f_type.
> > 
> > Is there anything more we should add here? Samba wants a capabilities
> > field, with things like sparse files, quotas, compression, encryption,
> > case preserving/sensitive.
> > 
> > Any thoughts?
> 
> "struct statfs" and "struct statfs64" have spare fields.  We could put
> the f_flag in there including a magic "this is a valid f_flag" flag,
> that distinguishes from the default zero value.

Ah so it does. We have 5 words spare. So we should have a version
number rather than just do a per-word hack each time. We could
probably pack the version number into a few bits of f_flag though.

--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html


[Index of Archives]     [Linux Ext4 Filesystem]     [Union Filesystem]     [Filesystem Testing]     [Ceph Users]     [Ecryptfs]     [AutoFS]     [Kernel Newbies]     [Share Photos]     [Security]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux Cachefs]     [Reiser Filesystem]     [Linux RAID]     [Samba]     [Device Mapper]     [CEPH Development]
  Powered by Linux