Btrfs devel - Aug 2012 - How to get Btrfs on 2nd partition of USB HDD to automount as read/write

Hello, 

The question below is based on 
https://lists.ubuntu.com/archives/xubuntu-users/2012-
August/004509.html

Thanks in advance for any help with the following question, 
including pointing me to some other info resource if needed.  

I have a user with an Xubuntu 12.04.1 laptop, 32-bit.  He needs to 
use a USB hard disk drive which has 2 partitions:  the 1st 
partition is NTFS and the 2nd partition is Btrfs.  

When he plugs in the hard drive, both partitions auto-mount OK, 
except that the Btrfs partition automounts read-only.  That is, the 
permissions of the directories in /dev are drwx------ for the NTFS 
and dr-xr-xr-x for the Btrfs.  

How can the OS be set up so that the Btrfs will automount 
read/write?  

The "dmesg" command shows the following on plug-in of the drive:  

[ 7253.520087] usb 2-4: new high-speed USB device number 11 using 
ehci_hcd
[ 7253.656344] scsi11 : usb-storage 2-4:1.0
[ 7256.651677] scsi 11:0:0:0: Direct-Access     TOSHIBA  External 
USB 3.0 0001 PQ: 0 ANSI: 6
[ 7256.654722] sd 11:0:0:0: Attached scsi generic sg2 type 0
[ 7256.656970] sd 11:0:0:0: [sdb] 1465149168 512-byte logical 
blocks: (750 GB/698 GiB)
[ 7256.660515] sd 11:0:0:0: [sdb] Write Protect is off
[ 7256.660534] sd 11:0:0:0: [sdb] Mode Sense: 1f 00 00 08
[ 7256.662509] sd 11:0:0:0: [sdb] No Caching mode page present
[ 7256.662523] sd 11:0:0:0: [sdb] Assuming drive cache: write 
through
[ 7256.668478] sd 11:0:0:0: [sdb] No Caching mode page present
[ 7256.668498] sd 11:0:0:0: [sdb] Assuming drive cache: write 
through
[ 7256.673838]  sdb: sdb1 sdb2
[ 7256.681474] sd 11:0:0:0: [sdb] No Caching mode page present
[ 7256.681493] sd 11:0:0:0: [sdb] Assuming drive cache: write 
through
[ 7256.681507] sd 11:0:0:0: [sdb] Attached SCSI disk
[ 7257.545702] device label partition_label devid 1 transid 19 
/dev/sdb2
[ 7257.546790] btrfs: disk space caching is enabled

Neither the "usbmount" nor "pmount" packages are installed,
but
"thunar-volman" is installed.  I did install "pmount" only
to find
that it appears to be meant to be invoked manually, so I un-
installed it again.  

"uname -rv" reports:  

 3.2.0-29-generic #46-Ubuntu SMP Fri Jul 27 17:04:05 UTC 2012

The "groups" command shows that the user is a member of the 
following (in addition to a group named after his username):  

 adm dialout fax cdrom floppy tape sudo dip video plugdev fuse 
lpadmin sambashare

The "mount" command shows for the Btrfs partition in question:  

 /dev/sdb2 on /media/[partition_label] type btrfs 
(rw,nosuid,nodev,uhelper=udisks)

(I have substituted [partition_label] for the partition label, 
which is all letters, no punctuation marks.)

Because "mount" shows "rw", does that mean that it is the 
configuration of Btrfs, not the configuration of automounting, that 
is at issue?  

Thanks again for any suggestions.  

-dg1727

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On Sun, Aug 19, 2012 at 2:51 PM, dg1727 <dg1727@hushmail.com>
wrote:
>
> permissions of the directories in /dev are drwx------ for the NTFS
> and dr-xr-xr-x for the Btrfs.
>
> How can the OS be set up so that the Btrfs will automount
> read/write?
try:

chmod u+w /path/to/btrfs/mount

... for whatever reason mkfs.btrfs created new subvolumes (but not
snapshots!) with 555 perms, which essentially says "writable to nobody
at all" ... IIRC, this was changed within the last year or so.

-- 

C Anthony
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On Sun, Aug 19, 2012 at 03:51:47PM -0400, dg1727 wrote:
> Hello, 
> 
> The question below is based on 
> https://lists.ubuntu.com/archives/xubuntu-users/2012-
> August/004509.html
> 
> Thanks in advance for any help with the following question, 
> including pointing me to some other info resource if needed.  
> 
> I have a user with an Xubuntu 12.04.1 laptop, 32-bit.  He needs to 
> use a USB hard disk drive which has 2 partitions:  the 1st 
> partition is NTFS and the 2nd partition is Btrfs.  
> 
> When he plugs in the hard drive, both partitions auto-mount OK, 
> except that the Btrfs partition automounts read-only.  That is, the 
> permissions of the directories in /dev are drwx------ for the NTFS 
> and dr-xr-xr-x for the Btrfs.  
> 
> How can the OS be set up so that the Btrfs will automount 
> read/write?  
   As Anthony points out, this is a property of the filesystem, not
the OS or the mount options. Just use chmod.

   (It''s only filesystems like FAT, which have no concept of
permissions, which have mount options to set permissions)

   Hugo.

-- 
=== Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk ==  PGP
key: 515C238D from wwwkeys.eu.pgp.net or http://www.carfax.org.uk
   --- Two things came out of Berkeley in the 1960s: LSD and Unix. ---   
                       This is not a coincidence.

On Sun, Aug 19, 2012 at 03:05:11PM -0500, C Anthony Risinger
wrote:
> On Sun, Aug 19, 2012 at 2:51 PM, dg1727 <dg1727@hushmail.com> wrote:
> > permissions of the directories in /dev are drwx------ for the NTFS
> > and dr-xr-xr-x for the Btrfs.
> >
> > How can the OS be set up so that the Btrfs will automount
> > read/write?
> 
> try:
> 
> chmod u+w /path/to/btrfs/mount
> 
> ... for whatever reason mkfs.btrfs created new subvolumes (but not
> snapshots!) with 555 perms, which essentially says "writable to nobody
> at all" ... IIRC, this was changed within the last year or so.
The issue with subvols pemr 0700 was indeed fixed, on the kernel side.

The problem with missing ''w'' (ie mode 555) on a freshly
mkfs''ed image is
still present and it''s the user-space tools (mkfs) proble. Patch has
been sent some time ago

http://www.spinics.net/lists/linux-btrfs/msg17909.html

The workaround is to chmod as you suggested and is permanent once done.


david
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On Tue, 21 Aug 2012 11:36:32 -0400 David Sterba <dave@jikos.cz> 
wrote:
>On Sun, Aug 19, 2012 at 03:05:11PM -0500, C Anthony Risinger 
>wrote:
>> On Sun, Aug 19, 2012 at 2:51 PM, dg1727 <dg1727@hushmail.com> 
>> wrote:
>> > permissions of the directories in /dev are drwx------ for the 
>> > NTFS and dr-xr-xr-x for the Btrfs.
>> >
>> > How can the OS be set up so that the Btrfs will automount
>> > read/write?
>> 
>> try:
>> 
>> chmod u+w /path/to/btrfs/mount
>> 
>> ... for whatever reason mkfs.btrfs created new subvolumes (but 
>> not snapshots!) with 555 perms, which essentially says "writable 
>> to nobody at all" ... IIRC, this was changed within the last 
>> year or so.
>
>The issue with subvols pemr 0700 was indeed fixed, on the kernel 
>side.
>
>The problem with missing ''w'' (ie mode 555) on a freshly
mkfs''ed
>image is still present and it''s the user-space tools (mkfs) 
>proble. Patch has been sent some time ago
>
>http://www.spinics.net/lists/linux-btrfs/msg17909.html
>
>The workaround is to chmod as you suggested and is permanent once 
>done.
Thanks a lot for these answers.  As an exercise, how would I track 
that patch so I can tell when it has been released?  Pointing me to 
a webpage that covers this would be fine.  

-dg1727 

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On Tue, Aug 21, 2012 at 03:28:22PM -0400, dg1727 wrote:
> Thanks a lot for these answers.  As an exercise, how would I track 
> that patch so I can tell when it has been released?  Pointing me to 
> a webpage that covers this would be fine.  
You can easily check that the patch appears in the main progs repo at

http://git.kernel.org/?p=linux/kernel/git/mason/btrfs-progs.git;a=summary

or you can clone the repo and check the git log directly.


david
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