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Re: utimensat and AT_EMPTY_PATH

On 04/10/2017 06:05 PM, Ian Pilcher wrote:

Given a file descriptor that refers to a symbolic link, is there a way
to call utimensat (or some other function) to update its timestamp?

I.e. what I would like to do is:

   utimensat(linkfd, "", times, AT_EMPTY_PATH);

Unlike futimens, utimensat *can* update the timestamp of a symlink
(verified with "strace touch -h ..."), but it doesn't seem to accept
AT_EMPTY_PATH.

Is there any non-racy way to do this?
Usually, it's possible to use the non-f, non-at system call variants with a /proc/fd/%d path. Those appear as symbolic links in the proc file system, but they actually are not, and the kernel will do the right thing even when operating on O_PATH descriptors. 

Florian
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