Re: [9fans] i/o on a hangup channel asymmetry

[Roman Shaposhnik]

On Jul 18, 2009, at 6:06 PM, erik quanstrom wrote:

On Sat Jul 18 14:41:02 EDT 2009, r...@sun.com wrote:

In the "mom, why sky is blue" department, here's a silly question:
is there any good reason that read(2) on a hangup channel returns

an error, while write(2) on a hangup channel terminates an application

(by generating a note, of course, which can be ignored, but still)?

hmm. from a quick read of port/sysfile.c, i think the precise behavior might depend on the underlying device. if devtab[m->c->type]->bread/ bwrite are (ultimately) based on qbread and qbwrite, i read qio as saying that neither should

generate a note.

perhaps i've been asleep at the swtch, but i don't recall seing writes
on closed channels terminate programs with a note.

Observe:

cpu% cat test2.c
#include <u.h>
#include <libc.h>
#include <stdio.h>

void notary(void *v, char* s)
{
    fprintf(stderr, "NOTE: %s\n", s);
    noted(NCONT);
}

int main()
{
    notify(&notary);

    while (1) {
       fprintf(stderr, "%d\n", write(1, "roman", 5));
       sleep(5000);
    }
    return 0;
}

cpu% 8c test2.c
cpu% 8l test2.8
cpu% { ./8.out | cat  } & { sleep 10 ; slay cat | rc }
5
roman5
romanNOTE:  sys: write on closed pipe pc=0x00001525
-1
NOTE:  sys: write on closed pipe pc=0x00001525
-1
NOTE:  sys: write on closed pipe pc=0x00001525
-1

Thanks,
Roman.