Date: Thu, 7 Apr 2011 19:16:44 -0700 From: Garrett Cooper <yanegomi@gmail.com> To: Jeremy Chadwick <freebsd@jdc.parodius.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: <BANLkTimB9XmkX3V7sMg5dBLSqz=Vxz7nEQ@mail.gmail.com> In-Reply-To: <20110408000025.GA16252@icarus.home.lan> References: <4D9DF375.4080506@FreeBSD.org> <BANLkTimAyh4-T0gQ1cuQn0nm8m7SHwW5iA@mail.gmail.com> <20110408000025.GA16252@icarus.home.lan>
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On Thu, Apr 7, 2011 at 5:00 PM, Jeremy Chadwick <freebsd@jdc.parodius.com> wrote: > 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 t= o 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 S= CSI 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 c= all 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. >> >> =A0 =A0 As a generic question / observation, maybe we should just >> implement 'errors=3Dremount-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. =A0:-) > > 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=3Dremount-ro"). > Why: > > Are there any conditions where ENODEV is returned to the underlying vfs > layer for things like unexpected hardware issues? =A0I would imagine the > latter would be ENXIO, but I'm not certain. =A0An 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 > =A0 the bus, or maybe even the user yanking the drive right in the > =A0 middle) -- could this ever return ENODEV? > 4. Kernel attempts re-mount, which also fails, or possibly panics > =A0 due to some underlying condition which nobody predicted > 5. User mails mailing list > > If I'm worrying over nothing, then perfect. =A0:-) =A0My 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. Yeah. It seems like something else like EINVAL (just an example -- probably a bad one) would be better. Also, please be careful as returning ENODEV seems to be UFS-specific: The following errors can occur for a ufs file system mount: [ENODEV] A component of ufs_args fspec does not exist. Also, Tom Rhodes has a similar change to what I suggested on the backburner, but it hasn't been 100% fleshed out yet. Thanks, -Garrett
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