Date: Mon, 13 Sep 1999 22:04:15 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: Tony Finch <fanf@demon.net> Cc: Tony Finch <fanf@demon.net>, hackers@FreeBSD.ORG Subject: Re: mounting a partition more than once Message-ID: <199909140504.WAA27333@apollo.backplane.com> References: <E11QZ03-000DDr-00@fanf.noc.demon.net> <199909132116.OAA25920@apollo.backplane.com> <E11Qe1j-000DRT-00@fanf.noc.demon.net>
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:Matthew Dillon <dillon@apollo.backplane.com> wrote:
:> :Tony Finch <fanf@demon.net> wrote:
:...
:>
:> Hmm... well, there is a problem here. I believe this will allow
:> you to open the underlying block device read-only as well as mount
:> the filesystem read-only. This will confuse the buffer cache badly.
:
:I don't think so -- spec_open checks whether the block device has been
:mounted in order to prevent this, and I made sure that that check
:remains in force except when spec_open is called by ffs_mountfs (by
:adding the FMOUNTING flag). I assumed that the buffer cache will
:handle multiple read-only mounts because it handles multiple userland
:reading file descriptors.
Ah, I see it now!
:> Also, this may not be the best place to put the code. It make sense
:> to be able to mount a block device multiple times in a read-only
:> fashion, but the code should be in the open for the block device
:> rather then in UFS/FFS, so it can be used with other filesystems
:> and for other purposes.
:
:Yes, it's evident that this is true because I had to hack around
:essentially the same test in both spec_open and ffs_mountfs; removing
:the checks down from ffs_mountfs so it relies on spec_mount to DTRT
:would be neater, I think.
:
:Tony.
:--
:f.a.n.finch dot@dotat.at fanf@demon.net e pluribus unix
Yes. I think this is the right track to take. The result will be
more useful to the system and probably a cleaner patch as well.
-Matt
Matthew Dillon
<dillon@backplane.com>
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