Filesystem specific mount options mixed with auto fs type

DISCUSSION Phillip Susi 3 participants 8 messages Oct 10, 2013 – Oct 11, 2013 Util-Linux package

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Phillip Susi

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2013-10-10 14:21 UTC #0 lore raw

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I came across an old bug report where the user had set the utf8 mount option in /etc/fstab on a floppy, presumably to apply to a fat filesystem, but when a disk formatted with ext2 was used, the mount failed sine ext2 doesn't support this option.

That got me wondering, how are you supposed to specify mount options with the auto fs type? Certainly you don't just have to limit the options to ones that are universal to all filesystems? But how to specify that these options are for fs A, and these for fs B?

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Matthias Schniedermeyer

2013-10-10 17:03 UTC #1 lore raw

Quoted 10 lines · Phillip Susi

I came across an old bug report where the user had set the utf8 mount option in /etc/fstab on a floppy, presumably to apply to a fat filesystem, but when a disk formatted with ext2 was used, the mount failed sine ext2 doesn't support this option.
That got me wondering, how are you supposed to specify mount options with the auto fs type? Certainly you don't just have to limit the options to ones that are universal to all filesystems? But how to specify that these options are for fs A, and these for fs B?

AFAIK "mount -s" is just for that case:

- man mount -
-s Tolerate sloppy mount options rather than failing. This will
ignore mount options not supported by a filesystem type. Not all filesystems support this option. This option exists for support of the Linux autofs-based automounter.
- man mount -

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Matthias

Phillip Susi

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2013-10-10 17:29 UTC #2 lore raw

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Quoted 6 lines · Matthias Schniedermeyer

AFAIK "mount -s" is just for that case:
- man mount - -s Tolerate sloppy mount options rather than failing. This will ignore mount options not supported by a filesystem type. Not all filesystems support this option. This option exists for support of the Linux autofs-based automounter. - man mount -

This doesn't seem to actually work. Trying to mount an ext2 fs with the utf8 option still fails with an unknown option error.

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Karel Zak

maintainer

2013-10-11 08:37 UTC #3 lore raw

Quoted 6 lines · Phillip Susi

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Quoted 2 lines · Matthias Schniedermeyer
AFAIK "mount -s" is just for that case:

Quoted 7 lines

Quoted 4 lines
- man mount - -s Tolerate sloppy mount options rather than failing. This will ignore mount options not supported by a filesystem type. Not all filesystems support this option. This option exists for support of the Linux autofs-based automounter. - man mount -
This doesn't seem to actually work. Trying to mount an ext2 fs with the utf8 option still fails with an unknown option error.

"sloppy" is userspace command line option and I guess it was introduced for NFS (nfs4, nfs, ...) and if I good remember nothing else uses this option.

There is also "silent" (MS_SILENT) kernel mount flag, but it's usually used to avoid unwanted printk() when superblok not found.

Notes:

* the "auto" fs type is usually used with generic mount options or with no options at all ("default" options)

* well designed filesystems allows to save the filesystem specific options to the FS superblock by some tune util (e.g. tune2fs)

* for removable media users usually use udisks based solutions

* mount by FS identifier

        LABEL=FOO       /mnt/floppy     vfat    utf8
        LABEL=BAR       /mnt/floppy     ext2    default

and then "mount LABEL= ... "

* for example NFS has nfsmount.conf where you can specify additional options, but I don't think it's a good idea to introduce this for all filesystems

Maybe we can improve mount(8) to test all entries from /etc/fstab with the same mountpoint (if you want to mount-by-mountpoint) until the filesystem will be mounted successfully. But I have doubts that we really need to resolve this very old disadvantage.

Karel

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 Karel Zak  <[email protected]>
 http://karelzak.blogspot.com

Phillip Susi

author

2013-10-11 13:45 UTC #4 lore raw

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Quoted 2 lines · Karel Zak

* well designed filesystems allows to save the filesystem specific options to the FS superblock by some tune util (e.g. tune2fs)

Unfortunately, fat isn't well designed.

Quoted 1 line

* for removable media users usually use udisks based solutions

That works as long as udisks picks the defaults they want, but then if they want a non default mount option ( or location ), they have to specify it in fstab.

Quoted 4 lines

* mount by FS identifier
LABEL=FOO /mnt/floppy vfat utf8 LABEL=BAR
/mnt/floppy ext2 default

That ties it to the specific volume.

Quoted 4 lines

Maybe we can improve mount(8) to test all entries from /etc/fstab with the same mountpoint (if you want to mount-by-mountpoint) until the filesystem will be mounted successfully. But I have doubts that we really need to resolve this very old disadvantage.

Maybe something like:

/dev/fd0 /mnt/floppy auto,vfat utf8
/dev/fd0 /mnt/floppy auto generic-options

The auto would trigger blkid to identify the filesystem, and then only if it matches one of the additional listed filesystems would that line be applied.

I suppose that would also require changing other utilities like udisks to understand it?

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Karel Zak

maintainer

2013-10-11 14:35 UTC #5 lore raw

Quoted 8 lines · Phillip Susi

Quoted 4 lines
Maybe we can improve mount(8) to test all entries from /etc/fstab with the same mountpoint (if you want to mount-by-mountpoint) until the filesystem will be mounted successfully. But I have doubts that we really need to resolve this very old disadvantage.
Maybe something like:
/dev/fd0 /mnt/floppy auto,vfat utf8

                       ^^^^^^^^^

This is unacceptable, fstab is de-facto standard. We have to be backwardly compatible.

Quoted 5 lines

/dev/fd0 /mnt/floppy auto generic-options
The auto would trigger blkid to identify the filesystem, and then only if it matches one of the additional listed filesystems would that line be applied.

I thought something like:

        /dev/fd0 /mnt/floppy    vfat    utf8
        /dev/fd0 /mnt/floppy    auto    default

and then try in loop all the filesystem types for the mountpoint (or make it smart and ask blkid for the type).

Karel

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 Karel Zak  <[email protected]>
 http://karelzak.blogspot.com

Phillip Susi

author

2013-10-11 14:40 UTC #6 lore raw

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Quoted 7 lines · Karel Zak

I thought something like:
/dev/fd0 /mnt/floppy vfat utf8 /dev/fd0 /mnt/floppy auto
default
and then try in loop all the filesystem types for the mountpoint (or make it smart and ask blkid for the type).

What would this do to other utilities? Would this confuse udisks or systemd or upstart's mountall?

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Karel Zak

maintainer

2013-10-11 17:17 UTC #7 lore raw

In reply to Phillip Susi

Quoted 3 lines · Phillip Susi

Maybe something like:
/dev/fd0 /mnt/floppy auto,vfat utf8

                       ^^^^^^^^

Note that I wasn't right in the previous email, the list of the fs-types in fstab is also supported by mount(8), but it's very rarely used (in last 10 years a remember only one report with this setup). It works like "-t fs1,fs2" on mount(8) command line.

I have doubts that anything else than mount(8) support this syntax.

Karel

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 Karel Zak  <[email protected]>
 http://karelzak.blogspot.com