xdg-document-portal: implement flock

[lufia]

I implemented flock operation of FUSE.

This is needed for Steam client.

• Steam prints "flock (FILE) LOCK_SH failed. errno = 38" errors for each the game that was moved to the external disk ValveSoftware/steam-for-linux#10829

Tested

I tested whether the new xdg-document-portal accepts flock(2) syscall with flock(1).

$ umount /run/user/60331/doc
$ meson compile -C _build
$ ./_build/document-portal/xdg-document-portal &

$ cd /run/user/60331/doc
$ touch lock.L
$ flock -n lock.L sleep 100

Then, within 100 seconds, I ran flock(1) in other terminal session.

$ flock -n lock.L ls || echo BAD
BAD

I checked blocking operations are rejected.

$ flock lock.L ls
flock: lock.L: Function not implemented

$ flock -s lock.L ls
flock: lock.L: Function not implemented

[swick]

Looks like this will block the entire document portal when any file is blocked due to flock.

[lufia]

Hi, @swick
I mitigated not to block entire document-portal by rejecting blocking operations of flock.
Steam client works well in my Arch Linux box.

@hfiguiere Thanks for your suggestion!

[GeorgesStavracas]

Thanks for the patch. Please squash the suggestion commit into a single commit.

[swick]

Supporting flock only for certain option is very suspicious to me. This needs review from someone who knows about fuse and filesystems.

[Dutt-A]

Hello,
I'm wondering if someone can again take a look at this branch and merge it in. Without this addition, the Steam flatpak is unable to handle adding another filesystem.

[swick]

@alexlarsson ^

[smcv]

Without this addition, the Steam flatpak is unable to handle adding another filesystem

You can give the unofficial Steam Flatpak app direct access to locations where you want to add an extra Steam library by completely exiting from Steam, and then using something like:

$ mkdir /media/other-disk/steam-library
$ flatpak override --user --filesystem=/media/other-disk/steam-library com.valvesoftware.Steam

before starting Steam again and selecting /media/other-disk/steam-library as your new Steam library. This avoids the performance overhead of going through a FUSE filesystem, as well as avoiding any limitations like the one fixed in this branch.

(documentation)

[Dutt-A]

Without this addition, the Steam flatpak is unable to handle adding another filesystem

You can give the unofficial Steam Flatpak app direct access to locations where you want to add an extra Steam library by completely exiting from Steam, and then using something like:

$ mkdir /media/other-disk/steam-library
$ flatpak override --user --filesystem=/media/other-disk/steam-library com.valvesoftware.Steam

before starting Steam again and selecting /media/other-disk/steam-library as your new Steam library. This avoids the performance overhead of going through a FUSE filesystem, as well as avoiding any limitations like the one fixed in this branch.

(documentation)

Upon using the override I precisely get the original errorno 38 (function not implemented) that lufia mentions here, and I believe that the additions are need to allow the line to work, unless I am misunderstanding something.

[chrisawi]

Upon using the override I precisely get the original errorno 38 (function not implemented) that lufia mentions here, and I believe that the additions are need to allow the line to work, unless I am misunderstanding something.

No, the override is sufficient by itself. You do need to restart Steam, and you may need to remove and re-add the library in Steam so it doesn't continue to use the portal path. That error means it's probably still going through the document portal.

Also, just to be clear, you need to modify the path to match your actual Steam library location; don't use literally /media/other-disk/steam-library.

[Dutt-A]

Upon using the override I precisely get the original errorno 38 (function not implemented) that lufia mentions here, and I believe that the additions are need to allow the line to work, unless I am misunderstanding something.

No, the override is sufficient by itself. You do need to restart Steam, and you may need to remove and re-add the library in Steam so it doesn't continue to use the portal path. That error means it's probably still going through the document portal.

Also, just to be clear, you need to modify the path to match your actual Steam library location; don't use literally /media/other-disk/steam-library.

Really? I'll take a look and try again in a few days (occupied with moving right now).

I actually recall that the override was working for me perfectly fine on the Fedora KDE spin, but somehow it has not been working for me on the Fedora Sway spin. Both installations should have me running on Wayland.

I appreciate the input.