[Bug network/984] Respond to changed resolv.conf in gethostbyname

["ebiggers3 at gmail dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=984

Eric Biggers <ebiggers3 at gmail dot com> changed:

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                 CC|                            |ebiggers3 at gmail dot com

--- Comment #11 from Eric Biggers <ebiggers3 at gmail dot com> ---
Please consider for inclusion in glibc the stat() patch used by Debian.  I
recently spent a long time tracking down a problem with hostname resolution in
a long-running process which ultimately turned out to be caused by glibc
caching an empty /etc/resolv.conf.  This can occur if the network configuration
is dynamic, e.g. managed by DHCP and NetworkManager.  From googling, it's
apparent that many different programs, such as web browsers (Firefox, Chromium,
etc.), have also run into this problem and have had to add hacks to work around
it.

Interestingly, in contrast with /etc/resolv.conf, glibc's resolver immediately
recognizes changes in /etc/hosts.  Furthermore, /etc/hosts is always read in
full.  It seems that if there is concern about performance of stat()ing
/etc/resolv.conf, there could be an optimization made to skip reading
/etc/hosts if it hasn't changed, thereby replacing about 5 system calls with 1.
 That would likely save more time per getaddrinfo() than is spent by stat()ing
/etc/resolv.conf an extra time.

Of course, the "correct" solution would be to use inotify to push changes only
when they actually happen.  Unfortunately, glibc doesn't have an opportunity to
do that.

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