PING 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. So, do you choose for my first pragmatic and non-intrusive patch, that lets mount_block_root() retry with MS_RDONLY if the file system returns EROFS (https://lkml.org/lkml/2014/6/18/468) or for the second one that forces all file-systems to return EACCES instead of EROFS. (https://lkml.org/lkml/2014/6/20/98). Best regards Philippe On Fri, Jun 20, 2014 at 10:39:22AM +0200, Philippe De Muyter wrote: > mount must return EACCES, not EROFS, when one attempts to mount a > read-only filesystem in read-write mode, but the file-system layer > only transmits the error given by the block layer, and many block > drivers return EROFS in that case, so let's fix it in do_mount. > > Actually it is only a small problem for a user using the mount(1) > command, because EROFS is actually a more explicit answer than > EACCES, but init/do_mounts.c checks only for EACCES, not EROFS, > to decide to retry to mount the root file-system in read-only mode, > and so we are left with an unbootable kernel, and with a cryptic > error message (*) if the root partition happens to be read-only > > (*): VFS: Cannot open root device "mmcblk0p2" or unknown-block(179,2): > error -30 > > Signed-off-by: Philippe De Muyter <phdm@xxxxxxxxx> > Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> > Cc: Dave Chinner <david@xxxxxxxxxxxxx> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Cc: linux-fsdevel@xxxxxxxxxxxxxxx > --- > fs/namespace.c | 2 ++ > 1 files changed, 2 insertions(+), 0 deletions(-) > > diff --git a/fs/namespace.c b/fs/namespace.c > index 182bc41..6291a3f 100644 > --- a/fs/namespace.c > +++ b/fs/namespace.c > @@ -2411,6 +2411,8 @@ long do_mount(const char *dev_name, const char *dir_name, > > retval = security_sb_mount(dev_name, &path, > type_page, flags, data_page); > + if (retval == -EROFS) > + retval = -EACCES; > if (!retval && !may_mount()) > retval = -EPERM; > if (retval) > -- > 1.7.5.3 -- Philippe De Muyter +32 2 6101532 Macq SA rue de l'Aeronef 2 B-1140 Bruxelles -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
