Re: [PATCH] mkfs.xfs: sanity check stripe geometry from blkid

Eric Sandeen
2020-05-15T21:07:00Z

On 5/15/20 3:54 PM, Eric Sandeen wrote:
> On 5/15/20 3:48 PM, Darrick J. Wong wrote:
>> On Fri, May 15, 2020 at 02:14:17PM -0500, Eric Sandeen wrote:
>>> We validate commandline options for stripe unit and stripe width, and
>>> if a device returns nonsensical values via libblkid, the superbock write
>>> verifier will eventually catch it and fail (noisily and cryptically) but
>>> it seems a bit cleaner to just do a basic sanity check on the numbers
>>> as soon as we get them from blkid, and if they're bogus, ignore them from
>>> the start.
>>>
>>> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
>>> ---
>>>
>>> diff --git a/libfrog/topology.c b/libfrog/topology.c
>>> index b1b470c9..38ed03b7 100644
>>> --- a/libfrog/topology.c
>>> +++ b/libfrog/topology.c
>>> @@ -213,6 +213,19 @@ static void blkid_get_topology(
>>> val = blkid_topology_get_optimal_io_size(tp);
>>> *swidth = val;
>>>
>>> + /*
>>> + * Occasionally, firmware is broken and returns optimal < minimum,
>>> + * or optimal which is not a multiple of minimum.
>>> + * In that case just give up and set both to zero, we can't trust
>>> + * information from this device. Similar to xfs_validate_sb_common().
>>> + */
>>> + if (*sunit) {
>>> + if ((*sunit > *swidth) || (*swidth % *sunit != 0)) {
>>
>> I feel like we're copypasting this sunit/swidth checking logic all over
>> xfsprogs
>
> That's because we are!
>
>> and yet we're still losing the stripe unit validation whackamole
>> game.
>
> Need moar hammers!
>
>> In the end, we want to check more or less the same things for each pair
>> of stripe unit and stripe width:
>>
>> * integer overflows of either value
>> * sunit and swidth alignment wrt sector size
>> * if either sunit or swidth are zero, both should be zero
>> * swidth must be a multiple of sunit
>>
>> All four of these rules apply to the blkid_get_toplogy answers for the
>> data device, the log device, and the realtime device; and any mkfs CLI
>> overrides of those values.
>>
>> IOWs, is there some way to refactor those four rules into a single
>> validation function and call that in the six(ish) places we need it?
>> Especially since you're the one who played the last round of whackamole,
>> back in May 2018. :)
>
> So .... I would like to do that refactoring. I'd also like to fix this
> with some expediency, TBH...
>
> Refactoring is going to be a little more complicated, I fear, because sanity
> on "what came straight from blkid" is a little different from "what came from
> cmdline" and has slightly different checks than "how does it fit into the
> superblock we just read?"
>
> This (swidth-vs-sunit-is-borken) is common enough that I wanted to just kill
> it with fire, and um ... make it all better/cohesive at some later date.
>
> I don't like arguing for expediency over beauty but well... here I am.

A little more context, failures like this are caught today, but only
in the validators, and it's very noisy and nonobvious when it happens.
And we seem to keep finding devices that are broken like this, so would be
nice to just ignore them and move on.

-Eric