On 5/15/14, 12:39 PM, David Sterba wrote:
> On Wed, May 14, 2014 at 05:07:04PM -0500, Eric Sandeen wrote:
>>>> @@ -125,7 +154,20 @@ int make_btrfs(int fd, const char *device, const char
>>>> *label,
>>>> memset(&super, 0, sizeof(super));
>>>>
>>>> num_bytes = (num_bytes / sectorsize) * sectorsize;
>>>> - uuid_generate(super.fsid);
>>>> + if (fs_uuid) {
>>>> + if (uuid_parse(fs_uuid, super.fsid) != 0) {
>>>> + fprintf(stderr, "could not parse UUID: %s\n", fs_uuid);
>>>> + ret = -EINVAL;
>>>> + goto out;
>>>> + }
>>>> + if (!test_uuid_unique(fs_uuid)) {
>>>> + fprintf(stderr, "non-unique UUID: %s\n", fs_uuid);
>>>> + ret = -EBUSY;
>>>> + goto out;
>>>> + }
>>>
>>> Why a second call to test_uuid_unique(fs_uuid) ?
>>
>> Because kdave said he thought it was worth being paranoid in an earlier
>> email,
>> if I understood him correctly.
>
> I'm thinking about it again. My original idea was not to easily allow
> to create a duplicate uuid to a regular user. But, if one uses --uuid
> already, that's something I can count as a willful action and any
> mistakes can be blamed on the user.
>
> If we end up with a warning, then the documentation should say how
> spectacularly it can blow up the system.
>
So, in my testing, I found that re-mkfsing a device with the same UUID lead
to weird & distant segfaults in other bits of code. Probably due to the
uuid cache? </handwave> - I didn't dig into it, because ...
... people didn't want to be able to create duplicate UUIDs, so I figured
the outright rejection of that was a trivial way to solve it ...
And like I mentioned, if you really want to recreate the same UUID, you
can mkfs twice. It doesn't take long. ;)
I dunno, maybe that's too lame. For a feature that upstream development
doesn't really seem to want, I'm not sure how much more effort I should
put into it?
-Eric
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