Create pidfile on activate

packaging/arch/PKGBUILD-git

@@ -1,7 +1,7 @@
 # Maintainer: John Ramsden <johnramsden [at] riseup [dot] net>
 
 pkgname=zedenv-git
-pkgver=r103.0f21e17
+pkgver=r148.d7d00f2
 pkgrel=1
 pkgdesc="Utility to manage Boot Environments using ZFS"
 arch=('any')

zedenv/cli/activate.py

@@ -1,6 +1,7 @@
 """List boot environments cli"""
 
 import sys
+import errno
 
 import click
 
@@ -346,19 +347,35 @@ def cli(boot_environment: str,
     except RuntimeError as err:
         ZELogger.log({"level": "EXCEPTION", "message": err}, exit_on_error=True)
 
-    boot_environment_root = zedenv.lib.be.root()
+    try:
+        with zedenv.lib.check.Pidfile() as pf:
+
+            boot_environment_root = zedenv.lib.be.root()
 
-    bootloader_set = zedenv.lib.be.get_property(
-        f"{boot_environment_root}/{boot_environment}", "org.zedenv:bootloader")
-    if not bootloader and bootloader_set:
-        bootloader = bootloader_set if bootloader_set != '-' else None
+            bootloader_set = zedenv.lib.be.get_property(
+                f"{boot_environment_root}/{boot_environment}", "org.zedenv:bootloader")
+            if not bootloader and bootloader_set:
+                bootloader = bootloader_set if bootloader_set != '-' else None
 
-    if noconfirm and not bootloader:
-        sys.exit("The '--noconfirm/-y' flag requires the bootloader option '--bootloader/-b'.")
+            if noconfirm and not bootloader:
+                sys.exit(
+                    "The '--noconfirm/-y' flag requires the bootloader option '--bootloader/-b'.")
 
-    zedenv_activate(boot_environment,
-                    boot_environment_root,
-                    verbose,
-                    bootloader,
-                    noconfirm,
-                    noop)
+            zedenv_activate(boot_environment,
+                            boot_environment_root,
+                            verbose,
+                            bootloader,
+                            noconfirm,
+                            noop)
+
+    except IOError as e:
+        if e[0] == errno.EPERM:
+            ZELogger.log({
+                "level": "EXCEPTION", "message":
+                    "You need root permissions to activate"
+            }, exit_on_error=True)
+    except zedenv.lib.check.ProcessRunningException as pr:
+        ZELogger.log({
+            "level": "EXCEPTION", "message":
+                f"Already running activate.\n {pr}"
+        }, exit_on_error=True)

zedenv/lib/check.py

@@ -7,6 +7,11 @@
 import pyzfscmds.system.agnostic
 
 import zedenv.lib.be
+from zedenv.lib.logger import ZELogger
+
+import os
+import sys
+import errno
 
 
 def startup_check():
@@ -21,3 +26,88 @@ def startup_check():
             pyzfscmds.system.agnostic.mountpoint_dataset("/").split("/")[0])
     except RuntimeError as err:
         raise RuntimeError(f"Couldn't get bootfs property of pool.\n{err}\n")
+
+
+class Pidfile:
+
+    """
+    Reference:
+    https://stackoverflow.com/a/23837022
+    """
+
+    def __init__(self, name="zedenv.pid", directory="/var/run"):
+        self.pidfile = os.path.join(directory, name)
+
+    def __enter__(self):
+        if os.path.exists(self.pidfile):
+
+            pid = None
+            with open(self.pidfile) as f:
+                pid = self._check()
+                if pid:
+                    self.pidfd = None
+                    raise ProcessRunningException(
+                        f'process already running in {self.pidfile} as {pid}')
+                else:
+                    os.remove(self.pidfile)
+
+            if pid:
+                ProcessRunningException(
+                    f'process already running in {self.pidfile} as {pid}')
+
+        try:
+            with open(self.pidfile, 'w+') as f:
+                f.write(str(os.getpid()))
+        except OSError as e:
+            ZELogger.log({
+                "level": "EXCEPTION", "message": f"Cannot write to pidfile {self.pidfile}"
+            }, exit_on_error=True)
+
+        return self
+
+    def __exit__(self, t, e, tb):
+        # return false to raise, true to pass
+        if t is None:
+            # normal condition, no exception
+            self._remove()
+            return True
+        elif isinstance(t, ProcessRunningException):
+            # do not remove the other process lockfile
+            return False
+        else:
+            # other exception
+            if self.pidfd:
+                # this was our lockfile, removing
+                self._remove()
+            return False
+
+    def _remove(self):
+        # removed pidfile
+        os.remove(self.pidfile)
+
+    def _check(self):
+        """check if a process is still running
+        the process id is expected to be in pidfile, which should exist.
+        if it is still running, returns the pid, if not, return False."""
+
+        try:
+            with open(self.pidfile, 'r') as f:
+                try:
+                    pidstr = f.read()
+                    pid = int(pidstr)
+                except ValueError:
+                    # not an integer
+                    return False
+                try:
+                    os.kill(pid, 0)
+                except OSError:
+                    # can't deliver signal to pid
+                    return False
+                else:
+                    return pid
+        except FileNotFoundError:
+            return False
+
+
+class ProcessRunningException(BaseException):
+    pass