[pacman-dev] About pacman and libalpm workflow

Rémy Oudompheng remyoudompheng at gmail.com
Sat May 21 05:15:39 EDT 2011

On 2011/5/21 ari edelkind <edelkind+arch-pacman at gmail.com> wrote:
>  - What's the general idea -- the program flow -- of the way it's
>    currently being implemented?  Pseudo-code would be perfect for
>    answering this, but really, anything with system-level details
>    will do (the "package signing proposal" is not current and does
>    not contain system-level details).

Hello Ari,

It's a bit difficult to answer that question, I don't exactly what
documentation sources there are out there. I'll try a rough draft, and
then you can ask more questions if you want. Also try to have a look
at pyalpm: it contains example scripts in Python that try to replicate
pacman 3.5 behaviour.

Here is how to use libalpm :
- initialize it (alpm_initialize)
- set options (alpm_option_set_*)
- register databases (alpm_db_register_sync)
- do something (many functions there)
- unregister databases
- release the library (alpm_release)

In the "do something" part, you may perform a transaction, that is,
installation or uninstallation of packages. Transactions are done as
follows :
- alpm_trans_init with proper options
- alpm_trans_add / alpm_trans_remove (says which packages you want to
add or remove)
- alpm_trans_prepare : this will resolve dependencies and conflicts
- alpm_trans_commit : this will download packages, check them (md5 or
signature), and install/remove them
- alpm_trans_release()

The functions that are called to check signature are
alpm_db_check_pgp_signature, alpm_pkg_check_pgp_signature. Options
make this check optional if needed.


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