Date: Thu, 7 Apr 2011 17:00:25 -0700 From: Jeremy Chadwick <freebsd@jdc.parodius.com> To: Garrett Cooper <yanegomi@gmail.com> Cc: freebsd-fs@freebsd.org, freebsd-scsi@freebsd.org, Andriy Gapon <avg@freebsd.org>, FreeBSD Hackers <freebsd-hackers@freebsd.org> Subject: Re: retry mounting with ro when rw fails Message-ID: <20110408000025.GA16252@icarus.home.lan> In-Reply-To: <BANLkTimAyh4-T0gQ1cuQn0nm8m7SHwW5iA@mail.gmail.com> References: <4D9DF375.4080506@FreeBSD.org> <BANLkTimAyh4-T0gQ1cuQn0nm8m7SHwW5iA@mail.gmail.com>
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On Thu, Apr 07, 2011 at 01:20:53PM -0700, Garrett Cooper wrote: > On Thu, Apr 7, 2011 at 10:25 AM, Andriy Gapon <avg@freebsd.org> wrote: > > > > [sorry for double post, it should have been "hackers" not "hardware"] > > > > Guys, > > could you please review and comment on the following patch? > > http://people.freebsd.org/~avg/mount-retry-ro.diff > > Thank you! > > > > The patch consists of two parts. > > > > The first part is in CAM/SCSI to make sure that ENODEV is consistently returned to > > signal that an operation is not supported by a device (in accordance to intro(2)) > > and specifically to return ENODEV on write attempt to a read-only or > > write-protected media. ?Making this change in SCSI should cover real SCSI devices, > > as well as ATAPI through ahci/siis/atapicam or similar, plus majority (all?) of > > USB Mass Storage devices. > > > > The second part is in vfs_mount code. ?The idea is to re-try a mount call if we > > get the ENODEV error, and mounting was not already in read-only mode, and there > > was no explicit rw or noro option; the second try is changed to ro. > > > > I did only basic testing with an SD card in write-protected mode and a USB > > card-reader. ?Since I am not very familiar with vfs_mount code I might have missed > > some important details. > > As a generic question / observation, maybe we should just > implement 'errors=remount-ro' (or a reasonable facsimile) like Linux > has in our mount(8) command? Doesn't look like NetBSD, OpenBSD, or > [Open]Solaris sported similar functionality. I was going to recommend exactly this. :-) I like the idea of Andriy's patch, but would feel more comfortable if it were only used if a mount option was specified (-o errors=remount-ro"). Why: Are there any conditions where ENODEV is returned to the underlying vfs layer for things like unexpected hardware issues? I would imagine the latter would be ENXIO, but I'm not certain. An example situation: 1. User inserts USB flash drive/etc. 2. User tries to mount disk R/W manually 3. Weird/bizarre hardware issue happens mid-mount (drive falling off the bus, or maybe even the user yanking the drive right in the middle) -- could this ever return ENODEV? 4. Kernel attempts re-mount, which also fails, or possibly panics due to some underlying condition which nobody predicted 5. User mails mailing list If I'm worrying over nothing, then perfect. :-) My other concern is whether or not this mechanism change could caused some sort of "infinite loop" within devd(8)/devctl(4) where the daemon gets very confused as to what's going on or some automated commands get run when they shouldn't. -- | Jeremy Chadwick jdc@parodius.com | | Parodius Networking http://www.parodius.com/ | | UNIX Systems Administrator Mountain View, CA, USA | | Making life hard for others since 1977. PGP 4BD6C0CB |
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