Messages in this thread | | | Date | Thu, 20 Oct 2022 12:30:39 +0200 | From | Petr Vorel <> | Subject | Re: v6.1-rc1: Regression in notification of sethostname changes |
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> On 19.10.22 14:31, Petr Vorel wrote: > >> Hi Torsten,
> >>> Hello Petr,
> >>> your commit
> >>> commit bfca3dd3d0680fc2fc7f659a152234afbac26e4d > >>> Author: Petr Vorel <pvorel@suse.cz> > >>> Date: Thu Sep 1 21:44:03 2022 +0200
> >>> kernel/utsname_sysctl.c: print kernel arch
> >>> Print the machine hardware name (UTS_MACHINE) in /proc/sys/kernel/arch.
> >>> This helps people who debug kernel with initramfs with minimal environment > >>> (i.e. without coreutils or even busybox) or allow to open sysfs file > >>> instead of run 'uname -m' in high level languages.
> >>> broke the notification mechanism between the sethostname syscall and the pollers of /proc/sys/kernel/hostname.
> >>> The table uts_kern_table is addressed within uts_proc_notify by the enum value, however no new enum value was added in "enum uts_proc".
> >>> I noticed the problem when journald-systemd failed to detect hostname changes made with the sethostname syscall (as used by the hostname tool). > >>> When setting the hostname through /proc/sys/kernel/hostname the poll notification was working.
> >> Thanks a lot for your report, working on a fix! > >> Andrew, Greg, sorry for a regression.
> > Hi Torsten,
> > could you please post exact steps to reproduce the problem. > > Although the required fix to add new enum into enum uts_proc is trivial, > > I was not able to reproduce the problem with 6.1.0-rc1 (actually > > 6.1.0-rc1-4.g1d716d8-default which contains few extra patches).
> > # hostname; hostnamectl hostname; cat /proc/sys/kernel/hostname > > opensuse-tumbleweed.20221001 > > opensuse-tumbleweed.20221001 > > opensuse-tumbleweed.20221001
> > # hostnamectl set-hostname foo; echo $? > > 0 > > # hostname; hostnamectl hostname; cat /proc/sys/kernel/hostname > > foo > > foo > > foo
> > # hostname bar; echo $? > > 0 > > # hostname; hostnamectl hostname; cat /proc/sys/kernel/hostname > > bar > > bar > > bar
> > # echo "baz" > /proc/sys/kernel/hostname > > # hostname; hostnamectl hostname; cat /proc/sys/kernel/hostname > > baz > > baz > > baz
> > # hostnamectl set-hostname foo; reboot > > After reboot it's 'foo'. > > What am I missing?
> > BTW I originally tested the feature only on dracut initramfs (with rapido [1]), > > which obviously bypass systemd. For a fix I'm creating rpm package (binrpm-pkg).
> The problem is happening in the systemd-journald poll notification. I was checking for the problem by attaching gdb to the running systemd-journald and setting a breakpoint to the server_cache_hostname function. This function is triggered via dispatch_hostname_change whenever the hostname changes. This is done via sd_event API in systemd.
> Here is an example program for this functionality without any further dependency:
> #include <poll.h> > #include <fcntl.h> > #include <stdbool.h> > #include <stdio.h> > #include <unistd.h>
> int main() > { > struct pollfd info;
> info.fd = open("/proc/sys/kernel/hostname", O_RDONLY); > info.events = 0; > info.revents = 0;
> while (true) { > int res = poll(&info, 1, -1); > if (res > 0) { > if (info.revents != 0) { > char buffer[64]; > gethostname(buffer, sizeof(buffer)); > printf("Hostname has changed to: %s\n", buffer); > } > } > } > }
Rigth, poll() is broken. Thanks a lot for a simple reproducer! I'll send a fix shortly.
Kind regards, Petr
> I have also attached this program.
> If you call this program and issue calls of the hostname utility to change the hostname some message should be printed.
> Torsten
> #include <poll.h> > #include <fcntl.h> > #include <stdbool.h> > #include <stdio.h> > #include <unistd.h>
> int main() > { > struct pollfd info;
> info.fd = open("/proc/sys/kernel/hostname", O_RDONLY); > info.events = 0; > info.revents = 0;
> while (true) { > int res = poll(&info, 1, -1); > if (res > 0) { > if (info.revents != 0) { > char buffer[64]; > gethostname(buffer, sizeof(buffer)); > printf("Hostname has changed to: %s\n", buffer); > } > } > } > }
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