gfs2: New gfs2_withdraw_helper

Currently, when a gfs2 filesystem is withdrawn, an "offline" uevent is
triggered that invokes gfs2-util's gfs2_withdraw_helper script.  The
purpose of this script is to deactivate the filesystem's block device so
that it can be withdrawn immediately, even before all the filesystem's
caches have been discarded.  The script provided by gfs2-utils never did
anything useful, and there was no way for it to report back its status
to the kernel.

To fix that, extend the gfs2_withdraw_helper mechanism so that the
script can report one of the following results by writing the
corresponding value into "/sys$DEVPATH/lock_module/withdraw":

 0 - The shared block device has been marked inactive.  Future write
     operations will fail.

 1 - The shared block device may still be active and carry out
     write operations.

If the "offline" uevent isn't reacted upon within the timeout configured
in /sys$DEVPATH/tune/withdraw_helper_timeout (default 5 seconds), the
event handler is assumed to have failed.

In addition, add an additional "errors=deactivate" mount option.

With these changes, if fatal errors are detected on a gfs2 filesystem
and the filesystem is mounted with the "errors=panic" option, the kernel
will panic immediately.  Otherwise, an attempt will be made to
deactivate the underlying block device.  If successful, the kernel will
release all cluster-wide locks immediately so that the rest of the
cluster can continue.  If unsuccessful, the kernel will either panic
("errors=deactivate"), or it will purge all filesystem I/O before
releasing all cluster-wide locks ("errors=withdraw").

Note that the gfs2_withdraw_helper script still needs to be fixed to
take advantage of these improvements.  It could be changed to use a
mechanism like LVM Persistent Reservations.  "dmsetup suspend" is not a
suitable mechanism as it infinitely postpones I/O operations, which may
prevent withdraw from completing.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

0 files changed, 0 insertions, 0 deletions