Re: [PATCH RFC] btrfs-progs: mkfs: optimize file descriptor usage in mkfs.btrfs

[David Sterba <dsterba@suse.cz>]

On Thu, Feb 01, 2024 at 07:19:15PM +1030, Qu Wenruo wrote:
> The problem is, even if we change the sequence, it doesn't make much
> difference.
> 
> There are several things involved, and most of them are out of our control:
> 
> - The udev scan is triggered on writable fd close().
> - The udev scan is always executed on the parent block device
>    Not the partition device.
> - The udev scan the whole disk, not just the partition
> 
> With those involved, changing the nested behavior would not change anything.
> 
> The write in another partition of the same parent block device can still
> triggered a scan meanwhile we're making fs on our partition.

So this means that creating ext4 on /dev/sda1 and btrfs on /dev/sda2 can
trigger the udev events? And when both mkfs utilities would lock the
device then running them concurrently will fail, right? This could
happen in installation tools that can create different filesystems at
the same time.

I wonder if we should add options to assert, skip locking or wait until
it's free.