tech-kern archive

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Old Index]

ptyfs terminals updating atime on open(2)


after messing a bit around with write(1), I've seen that ptyfs has a very
strange behaviour.
It updates in ptyfs_getattr() all times, including the access time. Thus,
even if you only open(2) a tty, its access time is being modified.
The appended (as in "bottom text") program shows that. Just run cc on it and
give it as argument the path of an idle pty (it has to be a ptyfs-pty!).

This breaks e.g. the behaviour of write, which always open's the tty
before stat'ing it, thus _always_ giving you the lowest-numbered login
terminal of the user, at least in my test cases that was the case (and its
the expected behaviour of it).
Please do not update write(1) now, I'll supply some other patches for it as
well I would have to remerge then, and the work now would perhaps be gone.

I didn't file a bug for this nor did I supply a fix because I don't know if
you really *can* fix it. This behaviour must be around for a while, perhaps
there are userland programs relying on it. Though they'll be broken anyway
when being started on a real terminal.

Regards, Julian

#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/stat.h>

main(int argc, char *argv[])
        struct stat s;
        int fd;

        if (argc != 2) {
                printf("a.out <filename>\n");
                return 1;
        if (!stat(argv[1], &s))
                printf("stat atime: %d\n", (int)s.st_atime);
        if ((fd = open(argv[1], O_RDONLY, 0)) != -1)
                if (fstat(fd, &s) != -1)
                        printf("open atime: %d\n", (int)s.st_atime);
        return 0;

Attachment: signature.asc
Description: PGP signature

Home | Main Index | Thread Index | Old Index