On Thu, Apr 26, 2012 at 02:45:54PM +0100, David Howells wrote:
Steve French [off-list ref] wrote:
quoted
I also would prefer that we simply treat the time granularity as part
of the superblock (mounted volume) ie returned on fstat rather than on
every stat of the filesystem. For cifs mounts we could conceivably
have different time granularity (1 or 2 second) on mounts to old
servers rather than 100 nanoseconds.
The question is whether you want to have to do a statfs in addition to a stat?
I suppose you can potentially cache the statfs based on device number.
That said, there are cases where caching filesystem-level info based on i_dev
doesn't work. OpenAFS springs to mind as that only has one superblock and
thus one set of device numbers, but keeps all the inodes for all the different
volumes it may have mounted there.
I don't know whether this would be a problem for CIFS too - say on a windows
server you fabricate P:, for example, by joining together several filesystems
(with junctions?). How does this appear on a Linux client when it steps from
one filesystem to another within a mounted share?
In the NFS case we do try to preserve filesystem boundaries as well as
we can--the protocol has an fsid field and the client creates a new
mount each time it sees it change. And the protocol defines time_delta
as a per-filesystem attribute (though, somewhat hilariously, there's
also a per-filesystem "homogeneous" attribute that a server can clear to
indicate the per-filesystem attributes might actually vary within the
filesystem.)
--b.
On Thu, Apr 26, 2012 at 9:28 AM, J. Bruce Fields [off-list ref] wrote:
On Thu, Apr 26, 2012 at 02:45:54PM +0100, David Howells wrote:
quoted
Steve French [off-list ref] wrote:
quoted
I also would prefer that we simply treat the time granularity as part
of the superblock (mounted volume) ie returned on fstat rather than on
every stat of the filesystem. For cifs mounts we could conceivably
have different time granularity (1 or 2 second) on mounts to old
servers rather than 100 nanoseconds.
The question is whether you want to have to do a statfs in addition to a stat?
I suppose you can potentially cache the statfs based on device number.
That said, there are cases where caching filesystem-level info based on i_dev
doesn't work. OpenAFS springs to mind as that only has one superblock and
thus one set of device numbers, but keeps all the inodes for all the different
volumes it may have mounted there.
I don't know whether this would be a problem for CIFS too - say on a windows
server you fabricate P:, for example, by joining together several filesystems
(with junctions?). How does this appear on a Linux client when it steps from
one filesystem to another within a mounted share?
In the NFS case we do try to preserve filesystem boundaries as well as
we can--the protocol has an fsid field and the client creates a new
mount each time it sees it change. And the protocol defines time_delta
as a per-filesystem attribute (though, somewhat hilariously, there's
also a per-filesystem "homogeneous" attribute that a server can clear to
indicate the per-filesystem attributes might actually vary within the
filesystem.)
Thank you for reminding me, I need to look at this case more ...
although cifs creates implicit submounts (as we traverse DFS referrals)
there are probably cases where we need to do the same thing as NFS
and look at the fsid so we don't run into a Windows server
exporting something with a "junction" (e.g. directory redirection to
a DVD drive for example) and thus cross file system volume boundaries.
--
Thanks,
Steve
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html