Re: mount_mfs: why chdir?

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

>> I think [chdir] should be done _after_ the mount() call,
> If you do it that way, there would be a race with an immediately
> following umount, which would fail if attemted between the mount and
> the chdir which follows.

That happens only if cwd is the mount-on directory (at least in 5.2);
if a process's cwd is in a subdir of the mount-on directory, its cwd
after the mount is still under the covered directory, not the covering
directory.  (I also would argue it's a bug that cwds equaling the
covered directory are silently moved to the covering directory, but
that's a separate issue.)

mlelstv pointed out upthread that 10.1 (and presumably current)
mount_mfs absolutifies relative mount-on paths before mounting, so all
that's needed is that the chdir happen after converting the path; I
haven't checked that (cvsweb seems to be handing out 403s at the
moment), but would assume it's so.

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