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Exec portal


                .----.      |          .----.
               /      \     |         /  __  \
               |    \\\\....^.........| /  \  |
 .-------------|   '----- argv[] ---> | | =----------------.
 { portal-exec |   ------ envp[] ---->| |== portal-spawner }
 '-------------|   .----open fds ---> | | =----------------'
               |   /////''''v'''''''''|  ''   |
                \.__./      |          \.__../
                            |

Run a program in another environment on the same machine by forwarding arguments, environment variables and open file descriptors through a single unix domain socket.

Example:

Start the spawner like this, providing the full path to an executable:

$ ./portal-spawner /usr/games/cowsay

This will create a unix domain socket by default named portal.sock in the local directory. As long as this socket is reachable by portal-exec, try the following in another terminal:

$ ./portal-exec moo
 _____
< moo >
 -----
        \   ^__^
         \  (oo)\_______
            (__)\       )\/\
                ||----w |
                ||     ||

stdin, stdout and stderr and the moo argument and all environment variables of portal-exec are transferred through portal.sock to the spawner process. It forks a worker process and then finally runs the specified executable cowsay with all args, envs and file descriptors set up. The exit code or exit signals are transferred back to portal-exec. As cowsay has the file descriptors originating from portal-exec, all output appears in its terminal.

Additional features:

You can also omit the executable when running portal-spawner or already provide arguments to a specified program. The arguments of portal-exec are appended to the arguments of portal-spawner putting together the full argv[] and executable in argv[0] passed to exeve.

You can change the portal.sock filename by setting a PORTAL_NAME prior to launching both portal-spawner and portal-exec. PORTAL_NAME itself is not transferred from exec to spawner.

Use cases:

The portal-spawner can run in a restricted environment or directly use something like bubblewrap to set one up on each invocation. Right now this is used in an experimental info-beamer package where arguments and crucially an dmabuf fd is forwarded from one process to another running in a squashfs overlay. As the overlay can remain active between multiple runs, the filesystem cache doesn't get invalidated as would be the case if overlay would be set up each run.