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Proper backlog handling in Unix pty backend.

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If the Seat that the pty backend is talking to starts to back up, then
we ought to temporarily stop reading from the pty device, to pass that
back-pressure on to whatever's running in the terminal.

Previously, this didn't matter because a Seat running a GUI terminal
never backed up anyway. But now it does, so we should support it all
the way through the system.
This commit is contained in:
Simon Tatham 2021-12-19 11:15:50 +00:00
parent 4721571b8b
commit f780a45c57
1 changed files with 14 additions and 5 deletions
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19
unix/pty.c
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@ -73,6 +73,7 @@ struct Pty {
int master_i, master_o, master_e;
Seat *seat;
size_t output_backlog;
char name[FILENAME_MAX];
pid_t child_pid;
int term_width, term_height;
@ -83,6 +84,8 @@ struct Pty {
Backend backend;
};
#define PTY_MAX_BACKLOG 32768
/*
* We store all the (active) PtyFd structures in a tree sorted by fd,
* so that when we get an uxsel notification we know which backend
@ -589,6 +592,7 @@ void pty_pre_init(void)
}
static void pty_try_wait(void);
static void pty_uxsel_setup(Pty *pty);
static void pty_real_select_result(Pty *pty, int fd, int event, int status)
{
@ -673,7 +677,9 @@ static void pty_real_select_result(Pty *pty, int fd, int event, int status)
perror("read pty master");
exit(1);
} else if (ret > 0) {
seat_output(pty->seat, !is_stdout, buf, ret);
pty->output_backlog = seat_output(
pty->seat, !is_stdout, buf, ret);
pty_uxsel_setup(pty);
}
} else if (event == SELECT_W) {
/*
@ -775,8 +781,10 @@ static void pty_uxsel_setup_fd(Pty *pty, int fd)
if (fd < 0)
return;
/* read from standard output and standard error pipes */
if (pty->master_o == fd || pty->master_e == fd)
/* read from standard output and standard error pipes, assuming
* we're not too backlogged */
if ((pty->master_o == fd || pty->master_e == fd) &&
pty->output_backlog < PTY_MAX_BACKLOG)
rwx |= SELECT_R;
/* write to standard input pipe if we have any data */
if (pty->master_i == fd && bufchain_size(&pty->output_data))
@ -1514,8 +1522,9 @@ static bool pty_sendok(Backend *be)
static void pty_unthrottle(Backend *be, size_t backlog)
{
/* Pty *pty = container_of(be, Pty, backend); */
/* do nothing */
Pty *pty = container_of(be, Pty, backend);
pty->output_backlog = backlog;
pty_uxsel_setup(pty);
}
static bool pty_ldisc(Backend *be, int option)