diff options
authorwm4 <wm4@nowhere>2020-05-15 16:35:44 +0200
committerwm4 <wm4@nowhere>2020-05-15 16:37:41 +0200
commit5ebb498b7a41863c369c8fda49344e6f4a6d4203 (patch)
parentc4d0d7a194bee56b4cc4b0b7fec4a81261decd01 (diff)
scripting: make socket FD number for subprocesses dynamic
Before this, we pretty much guaranteed that --mpv-ipc-fd=3 would be passed. The FD was hardcoded, so scripts started by this mechanism didn't need to actually parse the argument. Change this to using a mostly random FD number instead. I decided to do this because posix_spawnp() and the current replacement cannot "guarantee" a FD layout. posix_spawn_file_actions_adddup2() just runs dup2() calls, so it may be hard to set FD 3/4 if they are already used by something else. For example imagine trying to map: {.fd = 3, .src_fd = 4}, {.fd = 4, .src_fd = 3}, Then it'd do dup2(4, 3), dup2(3, 4) (reminder: dup2(src, dst)), and the end result is that FD 4 really maps to the original FD 4. While this was not a problem in the present code, it's too messy that I don't want to pretend it can always done this way without an unholy mess. So my assumption is that FDs 0-2 can be freely assigned because they're never closed (probably...), while for all other FDs only pass-through is reasonable.
2 files changed, 4 insertions, 9 deletions
diff --git a/DOCS/man/ipc.rst b/DOCS/man/ipc.rst
index fdf5daf9b6..4b808b9ff9 100644
--- a/DOCS/man/ipc.rst
+++ b/DOCS/man/ipc.rst
@@ -380,11 +380,6 @@ shebang and have the executable bit set.
When executed, a socket (the IPC connection) is passed to them through file
descriptor inheritance. The file descriptor is indicated as the special command
line argument ``--mpv-ipc-fd=N``, where ``N`` is the numeric file descriptor.
-Currently, this is hardcoded as ``--mpv-ipc-fd=3``, and the intention is that
-it will always be ``3``. (This was a compromise between keeping it as simple as
-possible, and not doing too much implicitly. Also, since there is a chance that
-this will change anyway, you should at least validate that you got the expected
The rest is the same as with a normal ``--input-ipc-server`` IPC connection. mpv
does not attempt to observe or other interact with the started script process.
diff --git a/player/scripting.c b/player/scripting.c
index bb4c93b60e..7b3f9afb3c 100644
--- a/player/scripting.c
+++ b/player/scripting.c
@@ -335,8 +335,8 @@ static int load_run(struct mp_script_args *args)
// Hardcode them (according to opts.fds[]), because we want to allow clients
// to hardcode them if they want. Sue me.
- char *fdopt = fds[1] >= 0 ? "--mpv-ipc-fd=3:4"
- : "--mpv-ipc-fd=3";
+ char *fdopt = fds[1] >= 0 ? mp_tprintf(80, "--mpv-ipc-fd=%d:%d", fds[0], fds[1])
+ : mp_tprintf(80, "--mpv-ipc-fd=%d", fds[0]);
struct mp_subprocess_opts opts = {
.exe = (char *)args->filename,
@@ -348,8 +348,8 @@ static int load_run(struct mp_script_args *args)
{.fd = 2, .src_fd = 2,},
// Just hope these don't step over each other (e.g. fds[1] is not
// below 4, if the std FDs are missing).
- {.fd = 3, .src_fd = fds[0], },
- {.fd = 4, .src_fd = fds[1], },
+ {.fd = fds[0], .src_fd = fds[0], },
+ {.fd = fds[1], .src_fd = fds[1], },
.num_fds = fds[1] >= 0 ? 5 : 4,
.detach = true,