infos = All information you want to know is in keys below
infos/author = Markus Raab elekt.nosp@m.ra@m.nosp@m.arkus.nosp@m.-raa.nosp@m.b.org
infos/licence = BSD
infos/provides = resolver
infos/needs =
infos/placements = rollback getresolver setresolver commit
infos/status = productive maintained specific unittest tested libc configurable nodep
infos/description =

The @ handles operating system dependent tasks. One task is the resolving of the filenames for user and system (hence its name)

We have an optimistic approach. Locking is only used to detect concurrent cooperative processes in the short moment between prepare and commit. A conflict will be raised in that situation. When processes do not lock the file it might be overwritten. This is unavoidable because such problems can only be detected in the commit phase when it is too late for rollbacks.

Resolving Files

Use following command to see to which file is resolved to:

kdb file <Elektra path you are interested in>

See the constants of this plugin for further information, that are:

system/elektra/modules/resolver/constants
system/elektra/modules/resolver/constants/ELEKTRA_VARIANT_SYSTEM
system/elektra/modules/resolver/constants/ELEKTRA_VARIANT_USER
system/elektra/modules/resolver/constants/KDB_DB_HOME
system/elektra/modules/resolver/constants/KDB_DB_SYSTEM
system/elektra/modules/resolver/constants/KDB_DB_USER
system/elektra/modules/resolver/constants/KDB_DB_SPEC
system/elektra/modules/resolver/constants/KDB_DB_DIR

The build-in resolving works like (with ~ and pwd resolved from system):

for spec with absolute path: path
for spec with relative path: KDB_DB_SPEC + path
for dir with absolute path: pwd + path (or above when path is found)
for dir with relative path: pwd + KDB_DB_DIR + path (or above when path is found)
for user with absolute path: ~ + path
for user with relative path: ~ + KDB_DB_USER + path
for system with absolute path: path
for system with relative path: KDB_DB_SYSTEM + path

Example

For an absolute path /example.ini, you might get following values:

for spec: /example.ini
for dir: pwd/example.ini
for user: ~/example.ini
for system: /example.ini

For an relative path example.ini, you might get following values:

for spec: /usr/share/elektra/specification/example.ini
for dir: pwd/.dir/example.ini
for user: ~/.config/example.ini
for system: /etc/kdb/example.ini

Variants

Many variants exist that additionally influence the lookup process, typically by using environment variables.

Environment variables are very simple for one-time usage but their maintenance in start-up scripts is problematic. Additionally, they are controlled by the user, so they cannot be trusted. So it is not recommended to use environment variables.

Note that the file permissions apply, so it might be possible for non-root to modify keys in system.

See COMPILE.md for a documentation of possible variants.

XDG Compatibility

The resolver is fully XDG compatible if configured with the variant:

xp, xh or xu for user (either using passwd, HOME or USER as fallback or any combination of these fallbacks)
x for system, no fallback necessary

Additionally KDB_DB_USER needs to be left unchanged as .config.

XDG_CONFIG_DIRS will be used to resolve system paths the following way:

if unset or empty /etc/xdg will be used instead
all elements are searched in order of importance
- if a file was found, the search process is stopped
- if no file was found, the least important element will be used for potential write attempts.

Reading Configuration

1.) If no update needed (unchanged modification time): ABORT 2.) remember the last stat time (last update)

Writing Configuration

0.) On empty configuration: remove the configuration file and ABORT 1.) Open the configuration file If not available recursively create directories and retry. #ifdef ELEKTRA_LOCK_MUTEX 1.) Try to lock a global mutex, if not possible -> conflict #endif #ifdef ELEKTRA_LOCK_FILE 1.) Try to lock the configuration file, if not possible -> conflict #endif 2.) Check the update time -> conflict 3.) Update the update time (in order to not self-conflict)