[PATCH 0/4] nsswitch.conf reloading refactoring

[Carlos O'Donell]

On 6/25/20 12:04 AM, DJ Delorie via Libc-alpha wrote:
> 
> The purpose of this sequence of patches is to allow /etc/nsswitch.conf
> to be dynamically reloaded if it changes while a process is running.
> Previously, nsswitch.conf is loaded once at first use, but long
> running programs and highly mobile devices have caused a need for a
> more dynamic approach.
> 
> The work was done by Florian and I, and I've kept our work separate.
> Florian wrote new implementations of the internal datastructures and
> parsers (patches 0001 through 0003), and I did the integration of
> those into the rest of the system (patch 0004).
> 
> The general idea is that there's a cache of "action lists" which
> correspond to the portion of nsswitch.conf after the ":".  There's an
> array of the current action lists indexed by database (i.e. "passwd"
> or "hosts") which points into the cache.  The action list refers to a
> list of loaded service modules, which have all needed ABI functions
> pre-loaded.
> 
> Since all the data is loaded once and never changed (since it's
> cached), it becomes read-only after load, so no atomics are required
> outside of the load code.
> 
> The rename of "service_user" to "action_list" was intentional, to
> ensure that all use cases were looked at during the conversion.
> 
> Tested on x86-64.  Also ran some manual tests which did "gethostname"
> while nsswitch changed between hosts and dns.  Also tested nscd
> similarly.
> 
> Version 1 :-)
> 
> [PATCH 1/4] nss: Introduce <nss_module.h>
>       Florian Weimer <fweimer@redhat.com>
> 
>    nss_module handles all dynamically loadable service modules and
>    their entry points.
> 
> [PATCH 2/4] <nss_action.h>: New abstraction for combining NSS modules
>       Florian Weimer <fweimer@redhat.com>
> 
>    nss_action handles the cache of action lists and action parsing.
> 
> [PATCH 3/4] nss: Implement <nss_database.h>
>       Florian Weimer <fweimer@redhat.com>
> 
>    nss_database controls overall reloading and stores the list of
>    currently active action lists for each service.
> 
> [PATCH 4/4] nsswitch: use new internal API
>       DJ Delorie <dj@redhat.com>
> 
>    Removing the old (now unneeded) core code, integrating all users of
>    the core code, and adding some remaining core functionality.
 
Thanks for taking this project on and making glibc more dynamic in
this regard with IdM data sources.

-- 
Cheers,
Carlos.