Elektra
0.8.16
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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.
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):
pwd
+ path (or above when path is found)pwd
+ KDB_DB_DIR + path (or above when path is found)For an absolute path /example.ini, you might get following values:
pwd
/example.iniFor an relative path example.ini, you might get following values:
pwd
/.dir/example.iniMany 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.
The resolver is fully XDG compatible if configured with the variant:
Additionally KDB_DB_USER needs to be left unchanged as .config
.
XDG_CONFIG_DIRS will be used to resolve system paths the following way:
1.) If no update needed (unchanged modification time): ABORT 2.) remember the last stat time (last update)
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)