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core/exec-invoke: split out maybe_inherit_stdout_from_stdin(), use exec_input_is_inheritable()

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Note that exec_input_is_inheritable() rightfully refuses EXEC_INPUT_FILE,
in which case std_output would have been reset in service_fix_stdio()
already.

While at it, use the generic fallback logic of first trying user manager
stdout when stdin is not writable.
This commit is contained in:
Mike Yuan
2025-12-17 23:23:22 +00:00
committed by Luca Boccassi
parent e04382384d
commit a8e1796b09
1 changed files with 45 additions and 32 deletions
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src/core/exec-invoke.c
+45 -32
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@@ -460,6 +460,41 @@ static bool can_inherit_stderr_from_stdout(const ExecContext *context) {
return true;
}
static int maybe_inherit_stdout_from_stdin(const ExecContext *context, ExecInput i) {
int r;
assert(context);
if (context->std_output != EXEC_OUTPUT_INHERIT)
return 0;
/* If input got downgraded, inherit the original value */
if (i == EXEC_INPUT_NULL && exec_input_is_terminal(context->std_input))
return open_terminal_as(exec_context_tty_path(context), O_WRONLY, STDOUT_FILENO);
if (!exec_input_is_inheritable(i))
goto fallback;
r = fd_is_writable(STDIN_FILENO);
if (r <= 0) {
if (r < 0)
log_warning_errno(r, "Failed to check if inherited stdin is writable for stdout, using fallback: %m");
else
log_warning("Inherited stdin is not writable for stdout, using fallback: %m");
goto fallback;
}
return RET_NERRNO(dup2(STDIN_FILENO, STDOUT_FILENO));
fallback:
/* If we are not started from PID 1 we just inherit STDOUT from our parent process. */
if (getppid() != 1)
return STDOUT_FILENO;
/* We need to open /dev/null here anew, to get the right access mode. */
return open_null_as(O_WRONLY, STDOUT_FILENO);
}
static int setup_output(
const ExecContext *context,
const ExecParameters *params,
@@ -498,19 +533,15 @@ static int setup_output(
}
i = fixup_input(context, params->flags & EXEC_APPLY_TTY_STDIN);
o = context->std_output;
if (fileno == STDERR_FILENO) {
ExecOutput e = context->std_error;
/* This expects the input and output are already set up */
/* Don't change the stderr file descriptor if we inherit all
* the way and are not on a tty */
if (e == EXEC_OUTPUT_INHERIT &&
o == EXEC_OUTPUT_INHERIT &&
i == EXEC_INPUT_NULL &&
!exec_input_is_terminal(context->std_input) &&
if (context->std_error == EXEC_OUTPUT_INHERIT &&
context->std_output == EXEC_OUTPUT_INHERIT &&
i == EXEC_INPUT_NULL && !exec_input_is_terminal(context->std_input) &&
getppid() != 1)
return fileno;
@@ -527,34 +558,16 @@ static int setup_output(
return RET_NERRNO(dup2(STDOUT_FILENO, fileno));
}
o = e;
o = context->std_error;
} else if (o == EXEC_OUTPUT_INHERIT) {
/* If input got downgraded, inherit the original value */
if (i == EXEC_INPUT_NULL && exec_input_is_terminal(context->std_input))
return open_terminal_as(exec_context_tty_path(context), O_WRONLY, fileno);
} else {
assert(fileno == STDOUT_FILENO);
/* If the input is connected to anything that's not a /dev/null or a data fd, inherit that... */
if (!IN_SET(i, EXEC_INPUT_NULL, EXEC_INPUT_DATA)) {
r = fd_is_writable(STDIN_FILENO);
if (r <= 0) {
if (r < 0)
log_warning_errno(r, "Failed to check if inherited stdin is writable for %s, falling back to /dev/null.",
fileno == STDOUT_FILENO ? "stdout" : "stderr");
else
log_warning("Inherited stdin is not writable for %s, falling back to /dev/null.",
fileno == STDOUT_FILENO ? "stdout" : "stderr");
return open_null_as(O_WRONLY, fileno);
}
return RET_NERRNO(dup2(STDIN_FILENO, fileno));
}
r = maybe_inherit_stdout_from_stdin(context, i);
if (r != 0)
return r;
/* If we are not started from PID 1 we just inherit STDOUT from our parent process. */
if (getppid() != 1)
return fileno;
/* We need to open /dev/null here anew, to get the right access mode. */
return open_null_as(O_WRONLY, fileno);
o = context->std_output;
}
switch (o) {