Re: POSIX violation by writeback error

Theodore Y. Ts'o
2018-09-25T22:46:21Z

On Tue, Sep 25, 2018 at 07:35:11PM +0200, Adam Borowski wrote:
> Isn't this what the snippet for O_TMPFILE in "man 2 open" does?:
>
> char path[PATH_MAX];
> fd = open("/path/to/dir", O_TMPFILE | O_RDWR,
> S_IRUSR | S_IWUSR);
>
> /* File I/O on 'fd'... */
>
> snprintf(path, PATH_MAX, "/proc/self/fd/%d", fd);
> linkat(AT_FDCWD, path, AT_FDCWD, "/path/for/file",
> AT_SYMLINK_FOLLOW);

Huh. I stand corrected. I had assumed O_TMPFILE worked like any
other file where the link count was zero, and linkat(2) wouldn't allow
this. But obviously, this does work. In fact, from the linkat(2) man
page, using:

linkat(fd, NULL, AT_FDCWD, "/path/for/file", AT_EMPTY_PATH);

is an even simpler way that doesn't /proc being mounted.

TIL...

- Ted