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Refactor tty transfer to be more deliberate

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This is a big cleanup to how tty transfer works. Recall that when job
control is active, we transfer the tty to jobs via tcsetpgrp().

Previously, transferring was done "as needed" in continue_job. That is, if
we are running a job, and the job wants the terminal and does not have it,
we will transfer the tty at that point.

This got pretty weird when running mixed pipelines. For example:

    cmd1 | func1 | cmd2

Here we would run `func1` before calling continue_job. Thus the tty
would be transferred by the nested function invocation, and also restored
by that invocation, potentially racing with tty manipulation from cmd1 or
cmd2.

In the new model, migrate the tty transfer responsibility outside of
continue_job. The caller of continue_job is then responsible for setting up
the tty. There's two places where this gets done:

1. In `exec_job`, where we run a job for the first time.

2. In `builtin_fg` where we continue a stopped job in the foreground.

Fixes #8699
This commit is contained in:
ridiculousfish
2022-02-13 13:12:18 -08:00
parent 3f585cddfc
commit df2cbe321c
8 changed files with 163 additions and 167 deletions
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14
src/postfork.cpp
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@@ -137,7 +137,7 @@ int execute_setpgid(pid_t pid, pid_t pgroup, bool is_parent) {
}
}
int child_setup_process(pid_t new_termowner, pid_t fish_pgrp, const job_t &job, bool is_forked,
int child_setup_process(pid_t claim_tty_from, const job_t &job, bool is_forked,
const dup2_list_t &dup2s) {
// Note we are called in a forked child.
for (const auto &act : dup2s.get_actions()) {
@@ -161,7 +161,7 @@ int child_setup_process(pid_t new_termowner, pid_t fish_pgrp, const job_t &job,
return err;
}
}
if (new_termowner != INVALID_PID && new_termowner != fish_pgrp) {
if (claim_tty_from >= 0 && tcgetpgrp(STDIN_FILENO) == claim_tty_from) {
// Assign the terminal within the child to avoid the well-known race between tcsetgrp() in
// the parent and the child executing. We are not interested in error handling here, except
// we try to avoid this for non-terminals; in particular pipelines often make non-terminal
@@ -170,12 +170,10 @@ int child_setup_process(pid_t new_termowner, pid_t fish_pgrp, const job_t &job,
// another process which may happen if we are run in the background with job control
// enabled. Note if stdin is not a tty, then tcgetpgrp() will return -1 and we will not
// enter this.
if (tcgetpgrp(STDIN_FILENO) == fish_pgrp) {
// Ensure this doesn't send us to the background (see #5963)
signal(SIGTTIN, SIG_IGN);
signal(SIGTTOU, SIG_IGN);
(void)tcsetpgrp(STDIN_FILENO, new_termowner);
}
// Ensure this doesn't send us to the background (see #5963)
signal(SIGTTIN, SIG_IGN);
signal(SIGTTOU, SIG_IGN);
(void)tcsetpgrp(STDIN_FILENO, getpid());
}
sigset_t sigmask;
sigemptyset(&sigmask);