Hi Eric, On 5/12/22, Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote: > Luis Chamberlain <mcgrof@xxxxxxxxxx> writes: > >> On Tue, May 03, 2022 at 01:27:44PM +0200, Jason A. Donenfeld wrote: >>> On Mon, May 02, 2022 at 05:43:21PM +0200, Lennart Poettering wrote: >>> > On Mo, 02.05.22 17:30, Jason A. Donenfeld (Jason@xxxxxxxxx) wrote: >>> > >>> > > Just wanted to double check with you that this change wouldn't break >>> > > how >>> > > you're using it in systemd for /proc/sys/kernel/hostname: >>> > > >>> > > https://github.com/systemd/systemd/blob/39cd62c30c2e6bb5ec13ebc1ecf0d37ed015b1b8/src/journal/journald-server.c#L1832 >>> > > https://github.com/systemd/systemd/blob/39cd62c30c2e6bb5ec13ebc1ecf0d37ed015b1b8/src/resolve/resolved-manager.c#L465 >>> > > >>> > > I couldn't find anybody else actually polling on it. Interestingly, >>> > > it >>> > > looks like sd_event_add_io uses epoll() inside, but you're not >>> > > hitting >>> > > the bug that Jann pointed out (because I suppose you're not poll()ing >>> > > on >>> > > an epoll fd). >>> > >>> > Well, if you made sure this still works, I am fine either way ;-) >>> >>> Actually... ugh. It doesn't work. systemd uses uname() to read the host >>> name, and doesn't actually read() the file descriptor after receiving >>> the poll event on it. So I guess I'll forget this, and maybe we'll have >>> to live with sysctl's poll() being broken. :( > > We should be able to modify calling uname() to act the same as reading > the file descriptor. How? That sounds like madness. read() takes a fd. uname() doesn't. Are you proposing we walk through the fds of the process calling uname() til we find a matching one and then twiddle it's private context state? I mean I guess that'd work, but... Jason
