According to the documentation in systemd.resource-control(5),
resource-control options may be used in mount, scope, service,
slice, socket and swap units.
While e.g. systemd.service(5) includes that information,
documentation for some other units does not.
The most problematic example is systemd.slice(5).
Its documentation states a slice unit may only contain [Install]
and [Unit] sections, while actually it may contain also a [Slice]
section with options from systemd.resource-control(5).
units/user/app.slice is an example of a slice unit having a [Slice]
section.
Today listen file descriptors created by socket unit don't get passed to
commands in Exec{Start,Stop}{Pre,Post}= socket options.
This prevents ExecXYZ= commands from accessing the created socket FDs to do
any kind of system setup which involves the socket but is not covered by
existing socket unit options.
One concrete example is to insert a socket FD into a BPF map capable of
holding socket references, such as BPF sockmap/sockhash [1] or
reuseport_sockarray [2]. Or, similarly, send the file descriptor with
SCM_RIGHTS to another process, which has access to a BPF map for storing
sockets.
To unblock this use case, pass ListenXYZ= file descriptors to ExecXYZ=
commands as listen FDs [4]. As an exception, ExecStartPre= command does not
inherit any file descriptors because it gets invoked before the listen FDs
are created.
This new behavior can potentially break existing configurations. Commands
invoked from ExecXYZ= might not expect to inherit file descriptors through
sd_listen_fds protocol.
To prevent breakage, add a new socket unit parameter,
PassFileDescriptorsToExec=, to control whether ExecXYZ= programs inherit
listen FDs.
[1] https://docs.kernel.org/bpf/map_sockmap.html
[2] https://lore.kernel.org/r/20180808075917.3009181-1-kafai@fb.com
[3] https://man.archlinux.org/man/socket.7#SO_INCOMING_CPU
[4] https://www.freedesktop.org/software/systemd/man/latest/sd_listen_fds.html
The setting currently puts limits on connections per IP address and
AF_UNIX CID. Let's extend it to cover AF_UNIX too, where it puts a limit
on connections per UID.
This is particularly useful for the various Accept=yes Varlink services
we now have, as it means, the number of per-user instance services
cannot grow without bounds.
This tries to add information about when each option was added. It goes
back to version 183.
The version info is included from a separate file to allow generating it,
which would allow more control on the formatting of the final output.
Doesn't really matter since the two unicode symbols are supposedly
equivalent, but let's better follow the unicode recommendations to
prefer greek small letter mu, as per:
https://www.unicode.org/reports/tr25
This is a rework of #24764 by Cristian Rodríguez
<crodriguez@owncloud.com>, which stalled.
Instead of assigning -1 we'll use a macro defined to INT_MAX however.
For some unit types we have hundreds of options, and the reader may easily miss
that more options are described in other pages. We already mentioned this in
the introduction and then at the top of the option list, but it can't hurt to
repeat the information.
Also, add an (almost empty) Options section for the unit types which don't have
any custom options. It is nicer to have the same page structure in all cases,
so people can jump between pages for different types more easily.
