On Mon, Feb 06, 2012 at 11:41:16PM +0100, Jan Kara wrote: > On Fri 03-02-12 16:22:23, Jerome Marchand wrote: > > > > When remounted without option specified, some filesystems keep the > > options that are already set (e.g. procfs, fat) and some reset them to > > default (e.g. devpts). > > Regarding options that are specified at remount, behavior of > > filesystems also differ: some apply them (procfs, devpts), some > > silently disregard them (e.g. fat) and some have a more elaborate > > behavior (e.g. xfs apparently allows a subset of options to be changed > > and issues warning if someone tries to change any other option). > > > > Is there any policy regarding what the correct behavior should be? > > This variety of behaviors tends to confuse mount utility which often > > does not show the correct option actually set after a remount and > > most certainly confuses the users as well. > > > > Here is a example of discrepancy between mount (/etc/mtab) and > > /proc/mounts: > > > > $ grep proc /proc/mounts > > /proc /proc proc rw,relatime 0 0 > > $ mount | grep proc > > proc on /proc type proc (rw) > > > > $ mount -o remount,hidepid=2 /proc/ > > $ grep proc /proc/mounts > > /proc /proc proc rw,relatime,hidepid=2 0 0 > > $ mount | grep proc > > proc on /proc type proc (rw,hidepid=2) > > > > $ mount -o remount /proc/ > > $ grep proc /proc/mounts > > /proc /proc proc rw,relatime,hidepid=2 0 0 > > $ mount | grep proc > > proc on /proc type proc (rw) > > > > And here is the discrepancy: mount does not show "hidepid=2" option > > that is actually still set and enforced. Note that mount also missed > > the relatime option to begin with. > I don't mind the discrepancy between /etc/mtab and /proc/mounts that much > (/proc/mounts is a fine replacement of /etc/mtab for me) but I agree that Fedora for example does not use /etc/mtab anymore. > handling of mount options on remount is a mess and IMHO it's made even > worse by mount(8) adding options from /etc/mtab to mount(2) syscall when > -o remount is specified. But realistically I can hardly imagine how to fix man mount: The remount functionality follows the standard way how the mount command works with options from fstab. It means the mount command doesn't read fstab (or mtab) only when a device and dir are fully specified. mount -o remount,rw /dev/foo /dir After this call all old mount options are replaced and arbitrary stuff from fstab is ignored, except the loop= option which is internally generated and maintained by the mount command. mount -o remount,rw /dir After this call mount reads fstab (or mtab) and merges these options with options from command line ( -o ). Note that mtab is a fallback solution when the mountpoint is not found in fstab, the mtab is not read by default. Anyway, libmount allows to specify how use the mount options from mtab and fstab. My plan is to add to mount(8) new command line options to override the current default, probably something like: --options-mode={ignore,append,prepend,replace} --options-source={fstab,mtab,none} so you will have a full control on options for mount(2) syscall. Karel -- Karel Zak <kzak@xxxxxxxxxx> http://karelzak.blogspot.com -- 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