Fix reuse of pty slave devices #2449
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tbodt
reviewed
Aug 31, 2024
| @@ -446,6 +446,7 @@ static ssize_t tty_read(struct fd *fd, void *buf, size_t bufsize) { | |||
| lock(&tty->lock); | |||
| if (tty->hung_up || pty_is_half_closed_master(tty)) { | |||
| unlock(&pids_lock); | |||
| err = -1; | |||
| // hang_up on the pty master. But the session leader may have a | ||
| // reference, and the pty master always has a reference. | ||
| if (tty->refcount - 1 == (tty->session ? 2 : 1)) { | ||
| tty->pty.other->hung_up = false; |
| // If userland's reference count on the pty slave is now 1, clear | ||
| // hang_up on the pty master. But the session leader may have a | ||
| // reference, and the pty master always has a reference. | ||
| if (tty->refcount - 1 == (tty->session ? 2 : 1)) { |
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I found this check a bit unsettling in the last PR but figured it could be fixed later. Seeing it again, I'm thinking much the same thing... Ideally we would define explicitly which references count for this and which ones don't, and with that knowledge the likely solution is to create a second refcount field for tracking just those.
Xcopz1
approved these changes
Sep 5, 2024
enkhjargal
approved these changes
Sep 20, 2024
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This should fix the problem brought up by @francoisvignon in my original work on #2387. At the time I wrote that I hadn't even thought about pty masters allowing serial reuse of the pty slave, and so it worked more like physical serial devices, where you don't want them to work after the modem hangs up.
This is definitely one of those less well documented and supported bits of functionality in ptys (there are many). But it seems like a good idea to support this because Linux does.