Messages in this thread | | | Date | Tue, 11 Sep 2018 00:55:50 +0100 | From | Al Viro <> | Subject | [WTF?] extremely old dead code |
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Folks, please tell me that I'm misreading the history here...
0.97: kernel/chr_dev/tty_ioctl.c:tty_ioctl(): + case FIONBIO: + if (arg) + file->f_flags |= O_NONBLOCK; + else + file->f_flags &= ~O_NONBLOCK; + return 0;
0.98.2: fs/ioctl.c:sys_ioctl(): + case FIONBIO: + on = get_fs_long((unsigned long *) arg); + if (on) + filp->f_flags |= O_NONBLOCK; + else + filp->f_flags &= ~O_NONBLOCK; + return 0;
Note that the call of ->f_op->ioctl() is in default: in the same switch, i.e. unreachable with cmd == FIONBIO.
0.98.3: kernel/chr_dev/tty_ioctl.c:tty_ioctl(): case FIONBIO: + arg = get_fs_long((unsigned long *) arg); if (arg) file->f_flags |= O_NONBLOCK; else wasn't that dead code by that point?
0.99.13k: kernel/chr_dev/tty_ioctl.c moves to drivers/char/tty_ioctl.c, tty_ioctl() essentially unchanged.
1.1.13: tty_ioctl() moves from drivers/char/tty_ioctl.c to drivers/char/tty_io.c, leaving some bits behind (as n_tty_ioctl()). FIONBIO handling is among the moved parts.
1.3.4: in tty_ioctl() case FIONBIO: - retval = verify_area(VERIFY_READ, (void *) arg, sizeof(long)); + retval = verify_area(VERIFY_READ, (void *) arg, sizeof(int));
1.3.28: same change happens in sys_ioctl().
2.1.4: handling moved to helper (fionbio())
In 2006: Alan writes a nice description of fionbio() +/** + * fionbio - non blocking ioctl + * @file: file to set blocking value + * @p: user parameter + * + * Historical tty interfaces had a blocking control ioctl before + * the generic functionality existed. This piece of history is preserved + * in the expected tty API of posix OS's. + * + * Locking: none, the open fle handle ensures it won't go away. + */ "generic functionality" bit refers to fcntl(2) (F_SETFL)
In 2010: the whole thing is moved to drivers/tty/tty_io.c
Hadn't that sucker been dead code since 0.98.2? What am I missing here? Note that this thing had quite a few functionality changes over those years; had they even been tested?
Confused and hoping to be told "Al, you're an idiot, here's an obvious way for that thing to be reached"...
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