Re: [PATCH] btrfs-prog: scrub: print message when scrubbing a read-only filesystem without r option

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

在 2024/7/4 09:43, David Sterba 写道:
> On Thu, Jul 04, 2024 at 08:56:47AM +0930, Qu Wenruo wrote:
>>> --- a/cmds/scrub.c
>>> +++ b/cmds/scrub.c
>>> @@ -957,7 +957,10 @@ static void *scrub_one_dev(void *ctx)
>>>    		warning("setting ioprio failed: %m (ignored)");
>>>
>>>    	ret = ioctl(sp->fd, BTRFS_IOC_SCRUB, &sp->scrub_args);
>>> -        pr_verbose(LOG_DEFAULT, "scrub ioctl devid:%llu ret:%d errno:%d\n",sp->scrub_args.devid, ret, errno);
>>> +	if (ret){
>>> +		pr_verbose(LOG_DEFAULT, "scrub on devid %llu failed ret=%d errno=%d (%m)\n",
>>> +			sp->scrub_args.devid, ret, errno);
>>> +	}
>>
>> Doing direct output inside a thread can lead to race of the output.
>
> We'd have to communicate the ioctl start errors back to the main thread,
> or rely on internal locking of printf, that it can race is possible but
> as long as the string is printed in one go we'll get only lines
> reordered.
>
>> And we do not know if the scrub ioctl would return error early or run
>> for a long long time, that's the dilemma.
>>
>> I'm wondering if it's possible to do a blkid/mountinfo based probe.
>> Then it would avoid the possible output race and error out earilier.
>
> We can detet read/write status of the block devices. I'm not sure about
> the mount info, what function can we use for that?
>

E.g, setmntent() and getmntent() used inside check_mounted_where()?

Since mntent structure provides mnt_opts, it should not be that hard to
find if the destination mount point is mounted ro?

Thanks,
Qu