Re: [md PATCH 09/36] md: make it easier to wait for bad blocks to be acknowledged.

[NeilBrown <neilb@suse.de>]

On Wed, 27 Jul 2011 01:04:15 +0900 Namhyung Kim <namhyung@gmail.com> wrote:

> NeilBrown <neilb@suse.de> writes:
> 
> > It is only safe to choose not to write to a bad block if that bad
> > block is safely recorded in metadata - i.e. if it has been
> > 'acknowledged'.
> >
> > If it hasn't we need to wait for the acknowledgement.
> >
> > We support that using rdev->blocked wait and
> > md_wait_for_blocked_rdev by introducing a new device flag
> > 'BlockedBadBlock'.
> >
> > This flag is only advisory.
> > It is cleared whenever we acknowledge a bad block, so that a waiter
> > can re-check the particular bad blocks that it is interested it.
> >
> > It should be set by a caller when they find they need to wait.
> > This (set after test) is inherently racy, but as
> > md_wait_for_blocked_rdev already has a timeout, losing the race will
> > have minimal impact.
> >
> > When we clear "Blocked" was also clear "BlockedBadBlocks" incase it
> > was set incorrectly (see above race).
> >
> > We also modify the way we manage 'Blocked' to fit better with the new
> > handling of 'BlockedBadBlocks' and to make it consistent between
> > externally managed and internally managed metadata.   This requires
> > that each raidXd loop checks if the metadata needs to be written and
> > triggers a write (md_check_recovery) if needed.  Otherwise a queued
> > write request might cause raidXd to wait for the metadata to write,
> > and only that thread can write it.
> >
> > Before writing metadata, we set FaultRecorded for all devices that
> > are Faulty, then after writing the metadata we clear Blocked for any
> > device for which the Fault was certainly Recorded.
> >
> > The 'faulty' device flag now appears in sysfs if the device is faulty
> > *or* it has unacknowledged bad blocks.  So user-space which does not
> > understand bad blocks can continue to function correctly.
> > User space which does, should not assume a device is faulty until it
> > sees the 'faulty' flag, and then sees the list of unacknowledged bad
> > blocks is empty.
> >
> > Signed-off-by: NeilBrown <neilb@suse.de>
> 
> Probably you also need this patch:
> 
> >From 76320c4fdaed91f26a083a9337bb5a5503300e0e Mon Sep 17 00:00:00 2001
> From: Namhyung Kim <namhyung@gmail.com>
> Date: Wed, 27 Jul 2011 00:59:26 +0900
> Subject: [PATCH] md: update documentation for md/rdev/state sysfs interface
> 
> Previous patches in the bad block series extended behavior of
> rdev's 'state' interface but lacked documentation update.
> Fix it.
> 
> Signed-off-by: Namhyung Kim <namhyung@gmail.com>

Applied, thanks.

NeilBrown


> ---
>  Documentation/md.txt |   14 +++++++++-----
>  1 files changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/Documentation/md.txt b/Documentation/md.txt
> index 923a6bddce7c..fc94770f44ab 100644
> --- a/Documentation/md.txt
> +++ b/Documentation/md.txt
> @@ -360,18 +360,20 @@ Each directory contains:
>          A file recording the current state of the device in the array
>  	which can be a comma separated list of
>  	      faulty   - device has been kicked from active use due to
> -                         a detected fault
> +                         a detected fault or it has unacknowledged bad
> +                         blocks
>  	      in_sync  - device is a fully in-sync member of the array
>  	      writemostly - device will only be subject to read
>  		         requests if there are no other options.
>  			 This applies only to raid1 arrays.
> -	      blocked  - device has failed, metadata is "external",
> -	                 and the failure hasn't been acknowledged yet.
> +	      blocked  - device has failed, and the failure hasn't been
> +			 acknowledged yet by the metadata handler.
>  			 Writes that would write to this device if
>  			 it were not faulty are blocked.
>  	      spare    - device is working, but not a full member.
>  			 This includes spares that are in the process
>  			 of being recovered to
> +	      write_error - device has ever seen a write error.
>  	This list may grow in future.
>  	This can be written to.
>  	Writing "faulty"  simulates a failure on the device.
> @@ -379,9 +381,11 @@ Each directory contains:
>  	Writing "writemostly" sets the writemostly flag.
>  	Writing "-writemostly" clears the writemostly flag.
>  	Writing "blocked" sets the "blocked" flag.
> -	Writing "-blocked" clears the "blocked" flag and allows writes
> -		to complete.
> +	Writing "-blocked" clears the "blocked" flags and allows writes
> +		to complete and possibly simulates an error.
>  	Writing "in_sync" sets the in_sync flag.
> +	Writing "write_error" sets writeerrorseen flag.
> +	Writing "-write_error" clears writeerrorseen flag.
>  
>  	This file responds to select/poll. Any change to 'faulty'
>  	or 'blocked' causes an event.