On Thu, 3 Jul 2014 18:29:19 +0200 Philippe De Muyter <phdm@xxxxxxxxx> wrote:
> On Wed, Jul 02, 2014 at 12:46:51PM -0700, Andrew Morton wrote:
> > On Fri, 27 Jun 2014 10:20:58 +0200 Philippe De Muyter <phdm@xxxxxxxxx> wrote:
> >
> > > Currently, the initial mount of the root file system by the linux
> > > kernel fails with a cryptic message instead of being retried with
> > > the MS_RDONLY flag set, when the device is read-only and the
> > > combination of block driver and filesystem driver yields EROFS.
> > >
> > > I do not know if POSIX mandates that mount(2) must fail with EACCES, nor
> > > if linux aims to strict compliance with POSIX on that point. Consensus
> > > amongst the messages that I have read so far seems to show that linux
> > > kernel hackers feel that EROFS is a more appropriate error code than
> > > EACCES in that case.
> >
> > Isn't the core problem that "the combination of block driver and
> > filesystem driver yields EROFS"? That the fs should instead be
> > returning EACCESS in this case?
>
> Does POSIX or Linux mandate that it should ?
>
> >
> > What fs and block driver are we talking about here, anyway?
>
> The problem happened to me with a f2fs filesystem on a sd-card that was
> accidentally write-protected and that was put in a SD-card slot (mmc block
> driver).
>
> I retested using mount(8) with a similar now intentionnaly write-protected
> sd card in a usb reader (usb_storage driver ?) with vfat, f2fs and ext4
> filesystems with the following results :
>
> mywdesk:~ # strace -e mount mount /dev/sdb1 /mnt
> mount("/dev/sdb1", "/mnt", "vfat", MS_MGC_VAL, NULL) = -1 EROFS (Read-only file system)
> mount: /dev/sdb1 is write-protected, mounting read-only
> mount("/dev/sdb1", "/mnt", "vfat", MS_MGC_VAL|MS_RDONLY, NULL) = 0
> +++ exited with 0 +++
> mywdesk:~ # umount /mnt
> mywdesk:~ # strace -e mount mount -t f2fs /dev/sdb2 /mnt
> mount("/dev/sdb2", "/mnt", "f2fs", MS_MGC_VAL, NULL) = -1 EROFS (Read-only file system)
> mount: /dev/sdb2 is write-protected, mounting read-only
> mount("/dev/sdb2", "/mnt", "f2fs", MS_MGC_VAL|MS_RDONLY, NULL) = 0
> +++ exited with 0 +++
> mywdesk:~ # umount /mnt
> mywdesk:~ # strace -e mount mount /dev/sdb3 /mnt
> mount("/dev/sdb3", "/mnt", "ext4", MS_MGC_VAL, NULL) = -1 EROFS (Read-only file system)
> mount: /dev/sdb3 is write-protected, mounting read-only
> mount("/dev/sdb3", "/mnt", "ext4", MS_MGC_VAL|MS_RDONLY, NULL) = 0
> +++ exited with 0 +++
> mywdesk:~ #
>
> All three file-systems (vfat, f2fs & ext4) yield EROFS.
>
> I also quickly grepped for occurences of EROFS under fs/, and found no check
> to replace EROFS by EACCES,
> while the same grep under drivers/{block,cdrom,ide,md,memstick, mtd,
> s390/block,scsi,usb} gives plenty of "return -EROFS;"
>
> So, if no filesystem driver replaces EROFS by EACCES and many block drivers
> return EROFS, it seems to me that many combinations will yield EROFS.
hm. I'm thinking that in an ideal world, those block drivers will
return -EACCES rather than -EROFS. You open() a read-only device for
rw, you get "permission denied".
Al, speak to us.
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