Re: deprecating /proc/mdstat (was: Re: mdadm bad blocks list)

[Shaohua Li <shli@kernel.org>]

On Thu, Jan 28, 2016 at 12:41:21PM +0100, Jens-U. Mozdzen wrote:
> Hello Neil & *,
> 
> Zitat von NeilBrown <nfbrown@novell.com>:
> >[...]
> >I'd like to deprecate /proc/mdstat.  It is not really easy to extend.
> 
> while I understand that /proc/mdstat's format might be considered "frozen"
> as in "do not confuse old scripts by new formats", I'd hate to see
> /proc/mdstat go away without a similar replacement: calling "mdadm" (or any
> other CLI) to gather that information is unruly expensive when all you have
> to do is "watch cat /proc/mdstat" to manually monitor critical operations.

That will not happen soon. Deprecating an interface takes years.
 
> >I'd recommend using "mdadm" to get status of an array, or examine file
> >in /sys.
> 
> If there's to be a "new mdstat" in /sys, I'd be fine with that. That would
> help migration for those "old scripts grep'ing /proc/mdstat" you rightfully
> care about.
> 
> I suggest to include a file format version information on line 1
> "/sys/.../mdstat", that way any client parsing such an interface could
> verify the file format first, and bail out if it doesn't support the
> currently presented format.

All the info you can get from /proc/mdstat can be found in /sys/xxx. There
isn't a central mdstat file in sysfs entry, each sysfs entry only export single
type info. Version info is uncessary, if we need add new info, we'd just add a
new sysfs entry.

though the /proc/mdstat will not be deprecated soon, it's highly encouraged app
switches to /sys. sysfs entry is easy to parse. And as Neil said, /proc/mdstat
is hard to extend, so new info will likely only appear in sysfs.

Thanks,
Shaohua