linux-kernel - Re: [PATCH 1/2] open: add close

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Message-ID: <82d34133-e174-efc3-48ed-332304028595@rasmusvillemoes.dk>
Date:   Tue, 21 May 2019 15:39:53 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Christian Brauner <christian@...uner.io>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-api@...r.kernel.org
Subject: Re: [PATCH 1/2] open: add close_range()

On 21/05/2019 13.34, Christian Brauner wrote:

> The performance is striking. For good measure, comparing the following
> simple close_all_fds() userspace implementation that is essentially just
> glibc's version in [6]:
> 
> static int close_all_fds(void)
> {
>         DIR *dir;
>         struct dirent *direntp;
> 
>         dir = opendir("/proc/self/fd");
>         if (!dir)
>                 return -1;
> 
>         while ((direntp = readdir(dir))) {
>                 int fd;
>                 if (strcmp(direntp->d_name, ".") == 0)
>                         continue;
>                 if (strcmp(direntp->d_name, "..") == 0)
>                         continue;
>                 fd = atoi(direntp->d_name);
>                 if (fd == 0 || fd == 1 || fd == 2)
>                         continue;
>                 close(fd);
>         }
> 
>         closedir(dir); /* cannot fail */
>         return 0;
> }

Before anybody copy-pastes this, please note that it lacks a check for
fd == dirfd(dir). If all of /proc/self/fd is returned in the first
getdents() syscall one won't notice, but...

Rasmus