linux-kernel - Re: getting mysterious (to me) EINVAL from inotify_rm

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Message-ID: <alpine.DEB.2.02.1605111643220.30706@pmeerw.net>
Date:	Wed, 11 May 2016 16:48:12 +0200 (CEST)
From:	Peter Meerwald-Stadler <pmeerw@...erw.net>
To:	Felix von Leitner <felix-linuxkernel@...e.de>
cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: getting mysterious (to me) EINVAL from inotify_rm_watch

Hi,

> I am trying to add inotify support to my tail implementation (for -F).
> This is what happens:
> 
>   inotify_init()                          = 4
>   inotify_add_watch(4, "/tmp/foo", IN_MODIFY) = 1
>   inotify_rm_watch(4, 1)                  = -1 EINVAL (Invalid argument)
>   inotify_add_watch(4, "/tmp/foo", IN_MODIFY) = 2
> 
> There is also some polling, some reading and some statting going on here, but
> those are on other descriptors than 4 so they should not matter).
> 
> Can somebody explain the EINVAL I'm getting from inotify_rm_watch to me?
> This is a stock kernel 4.5.0.

#include <stdio.h>
#include <sys/inotify.h>
int main() {
int fd, i, j;
printf("init %d\n", fd=inotify_init()); // 3
printf("add %d\n", i=inotify_add_watch(fd, "/tmp/foo", IN_MODIFY)); // 1
printf("rm %d\n", inotify_rm_watch(fd, i)); // 0
printf("add %d\n", j=inotify_add_watch(fd, "/tmp/foo", IN_MODIFY)); // 2
return 0;
}

Ubuntu kernel x86_64 4.4.0-21, seems to work here
so we have to guess what's going on between _add and _rm?

regards, p.

-- 

Peter Meerwald-Stadler
+43-664-2444418 (mobile)