Re: overlayfs: mounting overlayfs on top of overlayfs

[Jordi Pujol <jordipujolp@gmail.com>]

Hello,

Here are my comments about this patch:

I think "append" should also be prohibited in a read-only fs.

if (mask & (MAY_WRITE | MAY_APPEND))

About the readonly modification on the main filisystem mount, before this 
modification overlayfs already emited a warning message when mounting using a 
read only upperdir. Following is an old log:

+ COW_DIR=/tmp/TEST-sz5/COW-Mec
+ mount -t tmpfs -o ro tmpfs /tmp/TEST-sz5/COW-Mec
+ mount -t overlayfs -o rw,lowerdir=/tmp/TEST-sz5/ROOT-RO-
kei,upperdir=/tmp/TEST-sz5/COW-Mec overlayfs /tmp/TEST-sz5/ROOT-S1M
mount: block device overlayfs is write-protected, mounting read-only
(warning, return code 0)
 
+ mount -o remount,rw /tmp/TEST-sz5/ROOT-S1M
mount: cannot remount block device overlayfs read-write, is write-protected
(error, rc 32)

+ mount -l
overlayfs on /tmp/TEST-sz5/ROOT-S1M type overlayfs (ro,

but now, after appliying the last patch, the behaviour is very confused:
- there is no warning message when mounting overlayfs rw on a ro upperdir
- /proc/mounts shows overlayfs as a rw fs while really it is ro

+ mount -l
...
tmpfs on /tmp/TEST-Eo7/COW-uYW type tmpfs (ro)
overlayfs on /tmp/TEST-Eo7/ROOT-dAb type overlayfs (rw,lowerdir=/tmp/TEST-
Eo7/ROOT-RO-TfK,upperdir=/tmp/TEST-Eo7/ROOT-RO-TfK,upperdir=/tmp/TEST-Eo7/COW-
uYW)
+ mount -o remount,rw /tmp/TEST-Eo7/ROOT-dAb
mount: cannot remount block device overlayfs read-write, is write-protected

Sincerely, the previous behaviour was better,

Thanks,

Jordi Pujol

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