Re: [PATCH 2/2] libblkid: reopen floppy without O_NONBLOCK

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

15.12.2021 15:56, Karel Zak wrote:
> On Tue, Dec 14, 2021 at 05:24:44PM +0300, Vladimir Sementsov-Ogievskiy wrote:
>>> What does it mean didn't help?
>>
>> I tried it, but the bug remains as it was.. As I understand,
>> dropping O_NONBLOCK by fcntl just removes this flag, to change
>> further behavior of device to non-blocking. But it doesn't do any
>> additional actions in driver.
> 
> Hmm ...
> 
>>> The solution based on blkid_safe_open() means that we have to modify
>>> many applications. For example, systemd/udevd uses
>>>
>>>       fd = open(devnode, O_RDONLY|O_CLOEXEC|O_NONBLOCK);
>>>       r = blkid_probe_set_device(pr, fd, offset, 0);
>>
>> Hmm, yes, that's not very good :(
>>
>>>
>>> The same is probably in many other places (mkfs-like programs, etc.).
>>>
>>> What do you think?
>>>
>>
>> Maybe be we can get filename from fd reading it from /proc, then do
>> open() and than dup() to old fd.. But that's even more dirty to do
>> in a library call.
> 
> Yes, re-open() sounds like a possible way.
> 
> The dup() is not necessary. The library already support private FD for
> probing. See blkid_new_probe_from_filename() and BLKID_FL_PRIVATE_FD.
> 
> It's also often used when the library probe whole-disk device (when you
> probe sda1 than it also reads data from partition table on sda). In
> this case it opens a separate FD.
> 
> It's for floppies (0.001% of all cases). IMHO re-open is good enough and
> better than force changes in all applications :-)> 
> I'll try to prepare a patch and ask you for test/review. Thanks!
> 

Great!

-- 
Best regards,
Vladimir