[pacman-dev] [PATCH] Set an environment variable to indicate hooks support
thomas at archlinux.org
Tue Feb 23 18:37:56 UTC 2016
Am 22.02.2016 um 04:44 schrieb Allan McRae:
> On 22/02/16 00:40, Thomas Bächler wrote:
>> When replacing existing post_install and post_upgrade functionality
> with hooks, it
>> is necessary to ensure that pacman has already been upgraded. To allow
> a smooth
>> transition, export the ALPM_FEATURE_HOOKS variable with the value 1 in
> all processes
>> spawned by pacman.
>> An install scriptlet can fall back to old behaviour if this variable
> is not set,
>> but rely on pacman hooks if it is not set.
> This just makes install scriptlets more complicated... The alternative
> approach is for stupid distribution packagers to not start using hooks
> while (1) there is a major bug in them and (2) it has not been announced
> by the distribution that everyone should update to pacman-5.0 because we
> now require its features.
So, here is the problem: We need to ensure that everyone updated to
pacman 5.x before we can push an update that relies on hooks. When is
that? We don't know. Do we wait a week, a month, a year? Or 76.349 days?
If you upgrade your system with pacman<5, you will run a pacman version
without hooks during an upgrade that may already require hooks. This
will result in breakage.
Especially with a package like Linux, where serious bugs occur with the
current post_install process, we want to switch to hooks as fast as
possible - but doing so will cause more severe bugs unless everybody has
upgraded. This problem cannot be solved unless the install scriptlet is
As for the install scriptlet being "more complicated" - I think everyone
can live with the line
[[ -z $ALPM_FEATURE_HOOKS || $ALPM_FEATURE_HOOKS -lt 1 ]] && return
at the beginning of post_upgrade (yes, very complicated, I know).
>> lib/libalpm/util.c | 7 +++++++
>> 1 file changed, 7 insertions(+)
>> diff --git a/lib/libalpm/util.c b/lib/libalpm/util.c
>> index 001c042..86e3943 100644
>> --- a/lib/libalpm/util.c
>> +++ b/lib/libalpm/util.c
>> @@ -545,6 +545,11 @@ static int
> _alpm_chroot_read_from_child(alpm_handle_t *handle, int fd,
>> return 0;
>> +void _alpm_setup_child_environment()
>> + setenv("ALPM_FEATURE_HOOKS", "1", 1);
>> /** Execute a command with arguments in a chroot.
>> * @param handle the context handle
>> * @param cmd command to execute
>> @@ -618,6 +623,8 @@ int _alpm_run_chroot(alpm_handle_t *handle, const
> char *cmd, char *const argv,
>> + /* set up the child environment */
>> + _alpm_setup_child_environment();
> A whole function for one line...
I am preparing for the future. As an alternative, we can include the
setenv directly in _alpm_run_chroot and only have a one line change -
one that is hardly worth this discussion.
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