commands: add an update-config command

The update-config command is used to update the smb configuration
for an existing instance. The --watch option causes the command
to loop: monitoring the configuration JSON for change and reacting
to the change if it occurs.

Signed-off-by: John Mulligan <[email protected]>

Author: phlogistonjohn

sambacc/commands/config.py

@@ -16,12 +16,28 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>
 #
 
+import argparse
+import functools
+import logging
+import subprocess
 import sys
+import typing
 
+from sambacc import config
+from sambacc import samba_cmds
+from sambacc.simple_waiter import watch
 import sambacc.netcmd_loader as nc
 import sambacc.paths as paths
 
-from .cli import commands, setup_steps, Context
+from .cli import (
+    Context,
+    best_leader_locator,
+    best_waiter,
+    commands,
+    setup_steps,
+)
+
+_logger = logging.getLogger(__name__)
 
 
 @commands.command(name="print-config")
@@ -43,3 +59,96 @@ def import_config(ctx: Context) -> None:
 
     loader = nc.NetCmdLoader()
     loader.import_config(ctx.instance_config)
+
+
+def _update_config_args(parser: argparse.ArgumentParser) -> None:
+    parser.add_argument(
+        "--watch",
+        action="store_true",
+        help=("If set, watch the source for changes and update config."),
+    )
+
+
+def _read_config(ctx: Context) -> config.InstanceConfig:
+    cfgs = ctx.cli.config or []
+    return config.read_config_files(cfgs).get(ctx.cli.identity)
+
+
+def _update_config(
+    current: config.InstanceConfig,
+    previous: typing.Optional[config.InstanceConfig],
+    ensure_paths: bool = True,
+    notify_server: bool = True,
+) -> typing.Tuple[config.InstanceConfig, bool]:
+    """Compare the current and previous instance configurations. If they
+    differ, ensure any new paths, update the samba config, and inform any
+    running smbds of the new configuration.  Return the current config and a
+    boolean indicating if the instance configs differed.
+    """
+    # has the config changed?
+    changed = current != previous
+    # ensure share paths exist
+    if changed and ensure_paths:
+        for share in current.shares():
+            path = share.path()
+            if not path:
+                continue
+            _logger.info(f"Ensuring share path: {path}")
+            paths.ensure_share_dirs(path)
+    # update smb config
+    if changed:
+        _logger.info("Updating samba configuration")
+        loader = nc.NetCmdLoader()
+        loader.import_config(current)
+    # notify smbd of changes
+    if changed and notify_server:
+        subprocess.check_call(
+            list(samba_cmds.smbcontrol["smbd", "reload-config"])
+        )
+    return current, changed
+
+
+def _exec_if_leader(
+    ctx: Context,
+    cond_func: typing.Callable[..., typing.Tuple[config.InstanceConfig, bool]],
+) -> typing.Callable[..., typing.Tuple[config.InstanceConfig, bool]]:
+    """Run the cond func only on "nodes" that are the cluster leader."""
+    # CTDB status and leader detection is not changeable at runtime.
+    # we do not need to account for it changing in the updated config file(s)
+    @functools.wraps(cond_func)
+    def _call_if_leader(
+        current: config.InstanceConfig, previous: config.InstanceConfig
+    ) -> typing.Tuple[config.InstanceConfig, bool]:
+        with best_leader_locator(ctx.instance_config) as ll:
+            if not ll.is_leader():
+                _logger.info("skipping config update. node not leader")
+                return previous, False
+            _logger.info("checking for update. node is leader")
+            return cond_func(current, previous)
+
+    return _call_if_leader
+
+
+@commands.command(name="update-config", arg_func=_update_config_args)
+def update_config(ctx: Context) -> None:
+    _get_config = functools.partial(_read_config, ctx)
+    _cmp_func = _update_config
+
+    if ctx.instance_config.with_ctdb:
+        _logger.info("enabling ctdb support: will check for leadership")
+        _cmp_func = _exec_if_leader(ctx, _cmp_func)
+
+    if ctx.cli.watch:
+        _logger.info("will watch configuration source")
+        waiter = best_waiter(ctx.cli.config)
+        watch(
+            waiter,
+            ctx.instance_config,
+            _get_config,
+            _cmp_func,
+        )
+    else:
+        # we pass None as the previous config so that the command is
+        # not nearly always a no-op when run from the command line.
+        _cmp_func(_get_config(), None)
+    return