linux-2.6.25: 'mkdir -p' does not work with rootdir as mount point inside a read only filesystem

linux-2.6.25: 'mkdir -p' does not work with rootdir as mount point inside a read only filesystem

[Lothar Waßmann]

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Hi,

when trying to create a directory path with 'mkdir -p' with the root
being a mount point of a writeable filesystem that exists inside a
read-only file system, mkdir return -EROFS.

This was tested with the latest git-tree from:
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6

The last kernel I know of this has been working was 2.6.22.

E.g.:
|root@triton1:/# mount
|rootfs on / type rootfs (rw)
|/dev/root on / type jffs2 (ro)
|proc on /proc type proc (rw)
|sysfs on /sys type sysfs (rw)
|/dev/root on /dev/.static/dev type jffs2 (ro)
|tmpfs on /dev type tmpfs (rw,size=10240k,mode=755)
|tmpfs on /var type tmpfs (rw)
|tmpfs on /tmp type tmpfs (rw)
|devpts on /dev/pts type devpts (rw,gid=5,mode=620)
|tmpfs on /dev/shm type tmpfs (rw)
|root@triton1:/# mkdir -p /dev/.udev/db
|mkdir: Cannot create directory `/dev/': Read-only file system

While:
|root@triton1:/# cd /dev
|root@triton1:/# mkdir -p .udev/db
works as expected...

Has anyone else encountered this problem already?
I've searched the archives but could not find anything related to this
problem.



Lothar Waßmann
-- 
___________________________________________________________

Ka-Ro electronics GmbH | Pascalstraße 22 | D - 52076 Aachen
Phone: +49 2408 1402-0 | Fax: +49 2408 1402-10
Geschäftsführer: Matthias Kaussen
Handelsregistereintrag: Amtsgericht Aachen, HRB 4996

www.karo-electronics.de | info@karo-electronics.de
___________________________________________________________

Re: linux-2.6.25: 'mkdir -p' does not work with rootdir as mount point inside a read only filesystem

[Andrew Morton]

On Wed, 30 Apr 2008 16:50:20 +0200 Lothar Wa__mann <LW@KARO-electronics.de> wrote:

> Hi,

(y'know that ~4000 people read your email and hit 'n'?  Except for me?
That's one bug I'd like to get fixed)

> when trying to create a directory path with 'mkdir -p' with the root
> being a mount point of a writeable filesystem that exists inside a
> read-only file system, mkdir return -EROFS.
> 
> This was tested with the latest git-tree from:
> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6
> 
> The last kernel I know of this has been working was 2.6.22.
> 
> E.g.:
> |root@triton1:/# mount
> |rootfs on / type rootfs (rw)
> |/dev/root on / type jffs2 (ro)
> |proc on /proc type proc (rw)
> |sysfs on /sys type sysfs (rw)
> |/dev/root on /dev/.static/dev type jffs2 (ro)
> |tmpfs on /dev type tmpfs (rw,size=10240k,mode=755)
> |tmpfs on /var type tmpfs (rw)
> |tmpfs on /tmp type tmpfs (rw)
> |devpts on /dev/pts type devpts (rw,gid=5,mode=620)
> |tmpfs on /dev/shm type tmpfs (rw)
> |root@triton1:/# mkdir -p /dev/.udev/db
> |mkdir: Cannot create directory `/dev/': Read-only file system
> 
> While:
> |root@triton1:/# cd /dev
> |root@triton1:/# mkdir -p .udev/db
> works as expected...
> 
> Has anyone else encountered this problem already?
> I've searched the archives but could not find anything related to this
> problem.

I had a shot at scripting this, but for me, everything works OK.

#!/bin/sh
dd if=/dev/zero of=file1 bs=1M count=32
dd if=/dev/zero of=file2 bs=1M count=32
yes | mkfs -t ext2 file1
yes | mkfs -t ext2 file2
mkdir -p mountpoint
mount -o loop file1 mountpoint
mkdir mountpoint/dir
umount mountpoint
mount -o loop,ro file1 mountpoint
mount -o loop file2 mountpoint/dir
mkdir -p $(/bin/pwd)/mountpoint/dir/subdir


are you able to modify the above so that it demonstrates the failure?

Thanks.

Re: linux-2.6.25: 'mkdir -p' does not work with rootdir as mount point inside a read only filesystem

[NeilBrown]

On Fri, May 2, 2008 2:52 pm, Andrew Morton wrote:
> On Wed, 30 Apr 2008 16:50:20 +0200 Lothar Wa__mann
> <LW@KARO-electronics.de> wrote:
>
>> Hi,
>
> (y'know that ~4000 people read your email and hit 'n'?  Except for me?
> That's one bug I'd like to get fixed)

Tricky....

>
>> when trying to create a directory path with 'mkdir -p' with the root
>> being a mount point of a writeable filesystem that exists inside a
>> read-only file system, mkdir return -EROFS.

My guess is that you have an old/buggy version of mkdir.

What does
    mkdir --version

say?
Mine says:
mkdir (GNU coreutils) 6.10
Copyright (C) 2008 Free Software Foundation, Inc.
etc...

What does

   strace mkdir -p /dev/.udev/db

show ???

NeilBrown

Re: linux-2.6.25: 'mkdir -p' does not work with rootdir as mount point inside a read only filesystem

[Willy Tarreau]

On Fri, May 02, 2008 at 04:55:43PM +1000, NeilBrown wrote:
> On Fri, May 2, 2008 2:52 pm, Andrew Morton wrote:
> > On Wed, 30 Apr 2008 16:50:20 +0200 Lothar Wa__mann
> > <LW@KARO-electronics.de> wrote:
> >
> >> Hi,
> >
> > (y'know that ~4000 people read your email and hit 'n'?  Except for me?
> > That's one bug I'd like to get fixed)
> 
> Tricky....
> 
> >
> >> when trying to create a directory path with 'mkdir -p' with the root
> >> being a mount point of a writeable filesystem that exists inside a
> >> read-only file system, mkdir return -EROFS.
> 
> My guess is that you have an old/buggy version of mkdir.
> 
> What does
>     mkdir --version
> 
> say?
> Mine says:
> mkdir (GNU coreutils) 6.10
> Copyright (C) 2008 Free Software Foundation, Inc.
> etc...

I would bet this is the problem for the reporter.

I tried the same here, and cannot exhibit the problem. Just like the
reporter, my / is ro and /dev is rw :

# mkdir --version
mkdir (coreutils) 5.2.1
...

# uname -a
Linux alix-2C3 2.6.25-wt4-alix #3 Thu Apr 24 08:30:05 CEST 2008 i586 i586 i386 GNU/Linux

(this is essentially 2.6.25+squashfs+some geode patches)

# mount
/dev/sda4 on / type ext3 (ro,errors=continue,data=ordered)
/dev on /dev type tmpfs (rw,size=0k,nr_inodes=4096,mode=755)

# mkdir -p /dev/a/b/c
# ls -lad /dev/a/b/c
drwxr-xr-x  2 root root 40 Jan  3 00:49 /dev/a/b/c/

# rmdir -p /dev/a/b/c
rmdir: `/dev': Read-only file system
# strace mkdir -p /dev/a/b/c

stat64("/dev/a/b/c", 0xbf9175dc)        = -1 ENOENT (No such file or directory)
umask(0)                                = 022
open(".", O_RDONLY|O_LARGEFILE|O_DIRECTORY) = 3
chdir("/")                              = 0
mkdir("dev", 0755)                      = -1 EEXIST (File exists)
stat64("dev", {st_mode=S_IFDIR|0755, st_size=17080, ...}) = 0
chdir("dev")                            = 0
mkdir("a", 0755)                        = 0
chdir("a")                              = 0
mkdir("b", 0755)                        = 0
chdir("b")                              = 0
umask(022)                              = 0
mkdir("c", 0777)                        = 0
fchdir(3)                               = 0
close(3)                                = 0

Regards,
Willy

Re: linux-2.6.25: 'mkdir -p' does not work with rootdir as mount point inside a read only filesystem

[Lothar Waßmann]

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Hi,

Willy Tarreau writes:
> > My guess is that you have an old/buggy version of mkdir.
> > 
> > What does
> >     mkdir --version
> > 
> > say?
> > Mine says:
> > mkdir (GNU coreutils) 6.10
> > Copyright (C) 2008 Free Software Foundation, Inc.
> > etc...
> 
> I would bet this is the problem for the reporter.
> 
> I tried the same here, and cannot exhibit the problem. Just like the
> reporter, my / is ro and /dev is rw :
> 
I'm using busybox 1.0 (on an embedded PXA320 system).

> stat64("/dev/a/b/c", 0xbf9175dc)        = -1 ENOENT (No such file or directory)
> umask(0)                                = 022
> open(".", O_RDONLY|O_LARGEFILE|O_DIRECTORY) = 3
> chdir("/")                              = 0
> mkdir("dev", 0755)                      = -1 EEXIST (File exists)
> stat64("dev", {st_mode=S_IFDIR|0755, st_size=17080, ...}) = 0
> chdir("dev")                            = 0
> mkdir("a", 0755)                        = 0
> chdir("a")                              = 0
> mkdir("b", 0755)                        = 0
> chdir("b")                              = 0
> umask(022)                              = 0
> mkdir("c", 0777)                        = 0
> fchdir(3)                               = 0
> close(3)                                = 0
> 
This is what strace shows in my case:
mkdir("/", 0777)                        = -1 EEXIST (File exists)
stat64("/", {st_mode=S_IFDIR|0755, st_size=0, ...}) = 0
mkdir("/dev/", 0777)                    = -1 EROFS (Read-only file system)
umask(022)                              = 022
write(2, "mkdir: ", 7mkdir: )                  = 7
write(2, "Cannot create directory `/dev/\'", 31Cannot create directory `/dev/') = 31
write(2, ": Read-only file system\n", 24: Read-only file system
) = 24
io_submit(0x1, 0x1, 0xfbad2088 <unfinished ... exit status 1>


Lothar Waßmann
-- 
___________________________________________________________

Ka-Ro electronics GmbH | Pascalstraße 22 | D - 52076 Aachen
Phone: +49 2408 1402-0 | Fax: +49 2408 1402-10
Geschäftsführer: Matthias Kaussen
Handelsregistereintrag: Amtsgericht Aachen, HRB 4996

www.karo-electronics.de | info@karo-electronics.de
___________________________________________________________

Re: linux-2.6.25: 'mkdir -p' does not work with rootdir as mount point inside a read only filesystem

[Willy Tarreau]

On Mon, May 05, 2008 at 08:27:57AM +0200, Lothar Waßmann wrote:
> I'm using busybox 1.0 (on an embedded PXA320 system).

OK

> > stat64("/dev/a/b/c", 0xbf9175dc)        = -1 ENOENT (No such file or directory)
> > umask(0)                                = 022
> > open(".", O_RDONLY|O_LARGEFILE|O_DIRECTORY) = 3
> > chdir("/")                              = 0
> > mkdir("dev", 0755)                      = -1 EEXIST (File exists)
> > stat64("dev", {st_mode=S_IFDIR|0755, st_size=17080, ...}) = 0
> > chdir("dev")                            = 0
> > mkdir("a", 0755)                        = 0
> > chdir("a")                              = 0
> > mkdir("b", 0755)                        = 0
> > chdir("b")                              = 0
> > umask(022)                              = 0
> > mkdir("c", 0777)                        = 0
> > fchdir(3)                               = 0
> > close(3)                                = 0
> > 
> This is what strace shows in my case:
> mkdir("/", 0777)                        = -1 EEXIST (File exists)
> stat64("/", {st_mode=S_IFDIR|0755, st_size=0, ...}) = 0
> mkdir("/dev/", 0777)                    = -1 EROFS (Read-only file system)
> umask(022)                              = 022
> write(2, "mkdir: ", 7mkdir: )                  = 7
> write(2, "Cannot create directory `/dev/\'", 31Cannot create directory `/dev/') = 31
> write(2, ": Read-only file system\n", 24: Read-only file system
> ) = 24
> io_submit(0x1, 0x1, 0xfbad2088 <unfinished ... exit status 1>

So you should send this trace to the busybox maintainer. It
obviously exhibits a small but easily fixable bug in the
program ; it should check whether the directory exists in
case of error. It seems it only checks for EEXIST.

What puzzles me is why you have this problem only with a new kernel.
I suspect that previous ones did report EEXIST and now we report
EROFS for an existing directory on an ro fs.

Willy

Re: linux-2.6.25: 'mkdir -p' does not work with rootdir as mount point inside a read only filesystem

[Lothar Waßmann]

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Hi,

Willy Tarreau writes:
> > > open(".", O_RDONLY|O_LARGEFILE|O_DIRECTORY) = 3
> > > chdir("/")                              = 0
> > > mkdir("dev", 0755)                      = -1 EEXIST (File exists)
                                                   ^^^^^^
[...]
> > This is what strace shows in my case:
> > mkdir("/", 0777)                        = -1 EEXIST (File exists)
> > stat64("/", {st_mode=S_IFDIR|0755, st_size=0, ...}) = 0
> > mkdir("/dev/", 0777)                    = -1 EROFS (Read-only file system)
                                                 ^^^^^
> What puzzles me is why you have this problem only with a new kernel.
> I suspect that previous ones did report EEXIST and now we report
> EROFS for an existing directory on an ro fs.
> 
Interestingly your strace output showed a return value of EEXIST where
mine had EROFS.


Lothar Waßmann
-- 
___________________________________________________________

Ka-Ro electronics GmbH | Pascalstraße 22 | D - 52076 Aachen
Phone: +49 2408 1402-0 | Fax: +49 2408 1402-10
Geschäftsführer: Matthias Kaussen
Handelsregistereintrag: Amtsgericht Aachen, HRB 4996

www.karo-electronics.de | info@karo-electronics.de
___________________________________________________________

Re: linux-2.6.25: 'mkdir -p' does not work with rootdir as mount point inside a read only filesystem

[Willy Tarreau]

On Mon, May 05, 2008 at 09:08:00AM +0200, Lothar Waßmann wrote:
> Hi,
> 
> Willy Tarreau writes:
> > > > open(".", O_RDONLY|O_LARGEFILE|O_DIRECTORY) = 3
> > > > chdir("/")                              = 0
> > > > mkdir("dev", 0755)                      = -1 EEXIST (File exists)
>                                                    ^^^^^^
> [...]
> > > This is what strace shows in my case:
> > > mkdir("/", 0777)                        = -1 EEXIST (File exists)
> > > stat64("/", {st_mode=S_IFDIR|0755, st_size=0, ...}) = 0
> > > mkdir("/dev/", 0777)                    = -1 EROFS (Read-only file system)
>                                                  ^^^^^
> > What puzzles me is why you have this problem only with a new kernel.
> > I suspect that previous ones did report EEXIST and now we report
> > EROFS for an existing directory on an ro fs.
> > 
> Interestingly your strace output showed a return value of EEXIST where
> mine had EROFS.

Oh you're right! I did not notice. There's something odd here.
And I can reproduce it right now (2.6.25.1). I really have
EEXIST.

Willy

Re: linux-2.6.25: 'mkdir -p' does not work with rootdir as mount point inside a read only filesystem

[Lothar Waßmann]

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Hi,

Willy Tarreau writes:
> > Interestingly your strace output showed a return value of EEXIST where
> > mine had EROFS.
> 
> Oh you're right! I did not notice. There's something odd here.
> And I can reproduce it right now (2.6.25.1). I really have
> EEXIST.
> 
As I noted in my first message I have this problem with the kernel
from git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6
which is currently 2.6.26-rc1 and still exhibits this behaviour.

So, this problem obviously does not exist in the 2.6.25 release kernel
but would probably hit mainline in the 2.6.26 release.


Lothar Waßmann
-- 
___________________________________________________________

Ka-Ro electronics GmbH | Pascalstraße 22 | D - 52076 Aachen
Phone: +49 2408 1402-0 | Fax: +49 2408 1402-10
Geschäftsführer: Matthias Kaussen
Handelsregistereintrag: Amtsgericht Aachen, HRB 4996

www.karo-electronics.de | info@karo-electronics.de
___________________________________________________________

Re: linux-2.6.25: 'mkdir -p' does not work with rootdir as mount point inside a read only filesystem

[Al Viro]

On Mon, May 05, 2008 at 09:38:57AM +0200, Lothar Wa?mann wrote:
> Hi,
> 
> Willy Tarreau writes:
> > > Interestingly your strace output showed a return value of EEXIST where
> > > mine had EROFS.
> > 
> > Oh you're right! I did not notice. There's something odd here.
> > And I can reproduce it right now (2.6.25.1). I really have
> > EEXIST.
> > 
> As I noted in my first message I have this problem with the kernel
> from git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6
> which is currently 2.6.26-rc1 and still exhibits this behaviour.
> 
> So, this problem obviously does not exist in the 2.6.25 release kernel
> but would probably hit mainline in the 2.6.26 release.

Aye.  That's ro-bind fallout we'd not noticed; will fix...

And a fine example of the reasons why
	* relying on which particular errno value you get when several
are applicable is a Bad Idea(tm) and
	* changing the choice of the errno value in such situation might
be legal, but is to be done with care; sometimes it really has impact...

Re: linux-2.6.25: 'mkdir -p' does not work with rootdir as mount point inside a read only filesystem

[Dan Noé]

Andrew Morton wrote:
>> |root@triton1:/# mount
>> |rootfs on / type rootfs (rw)
>> |/dev/root on / type jffs2 (ro)
>> |proc on /proc type proc (rw)
>> |sysfs on /sys type sysfs (rw)
>> |/dev/root on /dev/.static/dev type jffs2 (ro)
>> |tmpfs on /dev type tmpfs (rw,size=10240k,mode=755)
>> |tmpfs on /var type tmpfs (rw)
>> |tmpfs on /tmp type tmpfs (rw)
>> |devpts on /dev/pts type devpts (rw,gid=5,mode=620)
>> |tmpfs on /dev/shm type tmpfs (rw)
>> |root@triton1:/# mkdir -p /dev/.udev/db
>> |mkdir: Cannot create directory `/dev/': Read-only file system
>>
>> While:
>> |root@triton1:/# cd /dev
>> |root@triton1:/# mkdir -p .udev/db
>> works as expected...
>>
>> Has anyone else encountered this problem already?
>> I've searched the archives but could not find anything related to this
>> problem.
> 
> I had a shot at scripting this, but for me, everything works OK.
> 
> #!/bin/sh
> dd if=/dev/zero of=file1 bs=1M count=32
> dd if=/dev/zero of=file2 bs=1M count=32
> yes | mkfs -t ext2 file1
> yes | mkfs -t ext2 file2
> mkdir -p mountpoint
> mount -o loop file1 mountpoint
> mkdir mountpoint/dir
> umount mountpoint
> mount -o loop,ro file1 mountpoint
> mount -o loop file2 mountpoint/dir
> mkdir -p $(/bin/pwd)/mountpoint/dir/subdir

Hmmm.  The thing you are doing differently is that the reporter's root 
filesystem is mounted read only but in your case (and the quick try I 
had at it) the read only file system is mounted below root.

However, I tried reproducing that scenario with a chroot and I still 
couldn't get it to happen.  No time to try a real root mount ro this 
morning but perhaps others can.

Cheers,
Dan

-- 
                     /--------------- - -  -  -   -   -
                     |  Dan Noé
                     |  http://isomerica.net/~dpn/