Date: Mon, 06 Mar 2000 15:14:52 -0800 From: Kirk McKusick <mckusick@flamingo.McKusick.COM> To: Erez Zadok <ezk@cs.columbia.edu> Cc: Alfred Perlstein <bright@wintelcom.net>, Terry Lambert <tlambert@primenet.com>, fs@freebsd.org, jkh@freebsd.org, Bruce Evans <bde@zeta.org.au> Subject: Re: changing mount options still can cause damage? Message-ID: <200003062314.PAA16884@flamingo.McKusick.COM> In-Reply-To: Your message of "Sun, 05 Mar 2000 14:12:30 EST." <200003051912.OAA01726@shekel.mcl.cs.columbia.edu>
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Date: Sun, 5 Mar 2000 14:12:30 -0500 (EST) From: Erez Zadok <ezk@cs.columbia.edu> To: Kirk McKusick <mckusick@flamingo.McKusick.COM> Cc: Alfred Perlstein <bright@wintelcom.net>, Terry Lambert <tlambert@primenet.com>, fs@FreeBSD.ORG, jkh@FreeBSD.ORG, Bruce Evans <bde@zeta.org.au> Subject: Re: changing mount options still can cause damage? In-reply-to: Your message of "Sat, 04 Mar 2000 11:34:00 PST." <200003041934.LAA16343@flamingo.McKusick.COM> In message <200003041934.LAA16343@flamingo.McKusick.COM>, Kirk McKusick writes: [...] > just as it would for a file open for writing). This seems > a slightly odd semantic for a file open for reading, so I > have not done it. Does anyone have any views on whether the > filesystem should be changed in this way on forcible > downgrades? > > Kirk Traditionally Unix file systems had all kind of odd semantics, but were considered reliable and stable. So *if* I had to choose b/t adding some odd semantics and keeping the f/s clean, I'd go for cleanliness. If, however, there is no clear winning option, then the next best thing would be to do one of the following: (1) add a new mount flag that can select among the choices. This option could be added to the mount(2) when it's doing a remount. We can select some default behavior for the flag, and let users turn it off if they want. (2) print some console message from there kernel upon remount, warning of any known open+unlinked files. BTW, can one remount read-only a f/s that's already remounted read-only? One (true hack) might be to keep the current remount semantics the same, but change them upon a second read-only remount. Erez. In contemplating these choices, I am inclined away from special mount flags or double remounting, as I think it would be hard to describe to a non-techinical person what these flags meant beyond down-grade cleanly and down-grade broken. The more I think about it the more I am inclined to say that non-forcible down-grade should fail if there are files open for writing or files open for reading with zero nlink counts. If a forcible downgrade is done, then all of these are vgone'd and the filesystem will be clean as a result. I had contemplated adding a -F (very forcible) unmount which unmounts without doing any additional I/O operations. Obviously such a filesystem would be dirty, but it would be useful if the disk (or NFS server) had died, and you just wanted the mount gone. But short of such an option, I think that a downgrade should leave the filesystem clean. Kirk To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-fs" in the body of the message
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