Hello!
On Fri, Apr 14, 2006 at 02:32:44PM -0700, Bryan Henderson wrote:
> >From my reading of the code it seems that fsid is composed of device's
> >minor/major and export point's inode ino.
> >I propose to replace (if supported by fs) device's minor/major by
> >some unique number returned by fs itself.
> >Should be no worse than what we have now.
> That's for a device-based filesystem. But isn't your proposal primarily
Yes. Device-based fs has root->s_dev. For non-device based (and for
device-based too, if they would like) - method to get some sort of
unique id to be used in the same way root->s_dev is used.
> about non-device-based filesystems, and replacing a user-supplied value
> with this filesystem identifier? It isn't so clear that that can't make
> things worse.
No, replacing whole fsid= with fs-supplied value would have implications like
that you mentioned - we might have two different points in filesystem
exported and we do not want those to have same id.
> But I don't actually remember the specific cases in which the fsid was
> considered insufficient; only that someone (probably Neil) did find that
> it was. (Before Linux had export IDs, you simply couldn't export a
> non-device-based filesystem at all, so we had to make a fake device on
> which the filesystem could "reside." The user managed the device number
> of that device as the filesystem ID).
We still have those "fake devices". In fact non-device based fs can set
REQUIRES_FS_DEV in fs_flags and it can be exported after that without
manually specifying fsid. (yeah, I tried). But distributed filesystems would
like to have same device id on different nodes.
Bye,
Oleg
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