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nspawn: add --console=autopipe mode 

By default we'll run a container in --console=interactive and
--console=read-only mode depending if we are invoked on a tty or not so
that the container always gets a /dev/console allocated, i.e is always
suitable to run a full init system /as those typically expect a
/dev/console to exist).

With the new --console=autopipe mode we do something similar, but
slightly different: when not invoked on a tty we'll use --console=pipe.
This means, if you invoke some tool in a container with this you'll get
full inetractivity if you invoke it on a tty but things will also be
very nicely pipeable. OTOH you cannot invoke a full init system like
this, because you might or might not become a /dev/console this way...

Prompted-by: #17070

(I named this "autopipe" rather than "auto" or so, since the default
mode probably should be named "auto" one day if we add a name for it,
and this is so similar to "auto" except that it uses pipes in the
non-tty case).
This commit is contained in:
Lennart Poettering 2020-09-17 16:26:14 +02:00
parent 335d2eadca
commit 10e8a60baa
2 changed files with 21 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

21
man/systemd-nspawn.xml
View File

@ -1370,15 +1370,18 @@
<listitem><para>Configures how to set up standard input, output and error output for the container
payload, as well as the <filename>/dev/console</filename> device for the container. Takes one of
<option>interactive</option>, <option>read-only</option>, <option>passive</option>, or
<option>pipe</option>. If <option>interactive</option>, a pseudo-TTY is allocated and made available
as <filename>/dev/console</filename> in the container. It is then bi-directionally connected to the
standard input and output passed to <command>systemd-nspawn</command>. <option>read-only</option> is
similar but only the output of the container is propagated and no input from the caller is read. If
<option>passive</option>, a pseudo TTY is allocated, but it is not connected anywhere. Finally, in
<option>pipe</option> mode no pseudo TTY is allocated, but the standard input, output and error
output file descriptors passed to <command>systemd-nspawn</command> are passed on — as they are — to
the container payload, see the following paragraph. Defaults to <option>interactive</option> if
<option>interactive</option>, <option>read-only</option>, <option>passive</option>,
<option>pipe</option> or <option>autopipe</option>. If <option>interactive</option>, a pseudo-TTY is
allocated and made available as <filename>/dev/console</filename> in the container. It is then
bi-directionally connected to the standard input and output passed to
<command>systemd-nspawn</command>. <option>read-only</option> is similar but only the output of the
container is propagated and no input from the caller is read. If <option>passive</option>, a pseudo
TTY is allocated, but it is not connected anywhere. In <option>pipe</option> mode no pseudo TTY is
allocated, but the standard input, output and error output file descriptors passed to
<command>systemd-nspawn</command> are passed on — as they are — to the container payload, see the
following paragraph. Finally, <option>autopipe</option> mode operates like
<option>interactive</option> when <command>systemd-nspawn</command> is invoked on a terminal, and
like <option>pipe</option> otherwise. Defaults to <option>interactive</option> if
<command>systemd-nspawn</command> is invoked from a terminal, and <option>read-only</option>
otherwise.</para>

12
src/nspawn/nspawn.c
View File

@ -256,10 +256,11 @@ STATIC_DESTRUCTOR_REGISTER(arg_sysctl, strv_freep);
static int handle_arg_console(const char *arg) {
if (streq(arg, "help")) {
puts("interactive\n"
"read-only\n"
puts("autopipe\n"
"interactive\n"
"passive\n"
"pipe");
"pipe\n"
"read-only");
return 0;
}
@ -277,6 +278,11 @@ static int handle_arg_console(const char *arg) {
"Proceeding anyway.");
arg_console_mode = CONSOLE_PIPE;
} else if (streq(arg, "autopipe")) {
if (isatty(STDIN_FILENO) > 0 && isatty(STDOUT_FILENO) > 0)
arg_console_mode = CONSOLE_INTERACTIVE;
else
arg_console_mode = CONSOLE_PIPE;
} else
return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Unknown console mode: %s", optarg);