Cleanup ZEDLETs

This commit factors out several common ZEDLET code blocks into
zed-functions.sh.  This shortens the length of the scripts, thereby
(hopefully) making them easier to understand and maintain.

In addition, this commit revamps the coding style used by the
scripts to be more consistent and (again, hopefully) maintainable.
It now mostly follows the Google Shell Style Guide.  I've tried to
assimilate the following resources:

  Google Shell Style Guide
  https://google-styleguide.googlecode.com/svn/trunk/shell.xml

  Dash as /bin/sh
  https://wiki.ubuntu.com/DashAsBinSh

  Filenames and Pathnames in Shell: How to do it Correctly
  http://www.dwheeler.com/essays/filenames-in-shell.html

  Common shell script mistakes
  http://www.pixelbeat.org/programming/shell_script_mistakes.html

Finally, this commit updates the exit codes used by the ZEDLETs to be
more consistent with one another.

All scripts run cleanly through ShellCheck <http://www.shellcheck.net/>.
All scripts have been tested on bash and dash.

Signed-off-by: Chris Dunlap <[email protected]>

1 files changed, 230 insertions, 0 deletions

diff --git a/cmd/zed/zed.d/zed-functions.sh b/cmd/zed/zed.d/zed-functions.sh
new file mode 100644
index 000000000..b42911b2e
--- /dev/null
+++ b/cmd/zed/zed.d/zed-functions.sh
@@ -0,0 +1,230 @@
+# zed-functions.sh
+#
+# ZED helper functions for use in ZEDLETs
+
+
+# Variable Defaults
+#
+: "${ZED_EMAIL_INTERVAL_SECS:=3600}"
+: "${ZED_EMAIL_VERBOSE:=0}"
+: "${ZED_LOCKDIR:="/var/lock"}"
+: "${ZED_RUNDIR:="/var/run"}"
+: "${ZED_SYSLOG_PRIORITY:="daemon.notice"}"
+: "${ZED_SYSLOG_TAG:="zed"}"
+
+ZED_FLOCK_FD=8
+
+
+# zed_check_cmd (cmd, ...)
+#
+# For each argument given, search PATH for the executable command [cmd].
+# Log a message if [cmd] is not found.
+#
+# Arguments
+#   cmd: name of executable command for which to search
+#
+# Return
+#   0 if all commands are found in PATH and are executable
+#   n for a count of the command executables that are not found
+#
+zed_check_cmd()
+{
+    local cmd
+    local rv=0
+
+    for cmd; do
+        if ! command -v "${cmd}" >/dev/null 2>&1; then
+            zed_log_err "\"${cmd}\" not installed"
+            rv=$((rv + 1))
+        fi
+    done
+    return "${rv}"
+}
+
+
+# zed_log_msg (msg, ...)
+#
+# Write all argument strings to the system log.
+#
+# Globals
+#   ZED_SYSLOG_PRIORITY
+#   ZED_SYSLOG_TAG
+#
+# Return
+#   nothing
+#
+zed_log_msg()
+{
+    logger -p "${ZED_SYSLOG_PRIORITY}" -t "${ZED_SYSLOG_TAG}" -- "$@"
+}
+
+
+# zed_log_err (msg, ...)
+#
+# Write an error message to the system log.  This message will contain the
+# script name, EID, and all argument strings.
+#
+# Globals
+#   ZED_SYSLOG_PRIORITY
+#   ZED_SYSLOG_TAG
+#   ZEVENT_EID
+#
+# Return
+#   nothing
+#
+zed_log_err()
+{
+    logger -p "${ZED_SYSLOG_PRIORITY}" -t "${ZED_SYSLOG_TAG}" -- "error:" \
+        "$(basename -- "$0"):" "${ZEVENT_EID:+"eid=${ZEVENT_EID}:"}" "$@"
+}
+
+
+# zed_lock (lockfile, [fd])
+#
+# Obtain an exclusive (write) lock on [lockfile].  If the lock cannot be
+# immediately acquired, wait until it becomes available.
+#
+# Every zed_lock() must be paired with a corresponding zed_unlock().
+#
+# By default, flock-style locks associate the lockfile with file descriptor 8.
+# The bash manpage warns that file descriptors >9 should be used with care as
+# they may conflict with file descriptors used internally by the shell.  File
+# descriptor 9 is reserved for zed_rate_limit().  If concurrent locks are held
+# within the same process, they must use different file descriptors (preferably
+# decrementing from 8); otherwise, obtaining a new lock with a given file
+# descriptor will release the previous lock associated with that descriptor.
+#
+# Arguments
+#   lockfile: pathname of the lock file; the lock will be stored in
+#     ZED_LOCKDIR unless the pathname contains a "/".
+#   fd: integer for the file descriptor used by flock (OPTIONAL unless holding
+#     concurrent locks)
+#
+# Globals
+#   ZED_FLOCK_FD
+#   ZED_LOCKDIR
+#
+# Return
+#   nothing
+#
+zed_lock()
+{
+    local lockfile="$1"
+    local fd="${2:-${ZED_FLOCK_FD}}"
+    local umask_bak
+    local err
+
+    [ -n "${lockfile}" ] || return
+    if ! expr "${lockfile}" : '.*/' >/dev/null 2>&1; then
+        lockfile="${ZED_LOCKDIR}/${lockfile}"
+    fi
+
+    umask_bak="$(umask)"
+    umask 077
+
+    # Obtain a lock on the file bound to the given file descriptor.
+    #
+    eval "exec ${fd}> '${lockfile}'"
+    err="$(flock --exclusive "${fd}" 2>&1)"
+    if [ $? -ne 0 ]; then
+        zed_log_err "failed to lock \"${lockfile}\": ${err}"
+    fi
+
+    umask "${umask_bak}"
+}
+
+
+# zed_unlock (lockfile, [fd])
+#
+# Release the lock on [lockfile].
+#
+# Arguments
+#   lockfile: pathname of the lock file
+#   fd: integer for the file descriptor used by flock (must match the file
+#     descriptor passed to the zed_lock function call)
+#
+# Globals
+#   ZED_FLOCK_FD
+#   ZED_LOCKDIR
+#
+# Return
+#   nothing
+#
+zed_unlock()
+{
+    local lockfile="$1"
+    local fd="${2:-${ZED_FLOCK_FD}}"
+    local err
+
+    [ -n "${lockfile}" ] || return
+    if ! expr "${lockfile}" : '.*/' >/dev/null 2>&1; then
+        lockfile="${ZED_LOCKDIR}/${lockfile}"
+    fi
+
+    # Release the lock and close the file descriptor.
+    #
+    err="$(flock --unlock "${fd}" 2>&1)"
+    if [ $? -ne 0 ]; then
+        zed_log_err "failed to unlock \"${lockfile}\": ${err}"
+    fi
+    eval "exec ${fd}>&-"
+}
+
+
+# zed_rate_limit (tag, [interval])
+#
+# Check whether an event of a given type [tag] has already occurred within the
+# last [interval] seconds.
+#
+# This function obtains a lock on the statefile using file descriptor 9.
+#
+# Arguments
+#   tag: arbitrary string for grouping related events to rate-limit
+#   interval: time interval in seconds (OPTIONAL)
+#
+# Globals
+#   ZED_EMAIL_INTERVAL_SECS
+#   ZED_RUNDIR
+#
+# Return
+#   0 if the event should be processed
+#   1 if the event should be dropped
+#
+# State File Format
+#   time;tag
+#
+zed_rate_limit()
+{
+    local tag="$1"
+    local interval="${2:-${ZED_EMAIL_INTERVAL_SECS}}"
+    local lockfile="zed.zedlet.state.lock"
+    local lockfile_fd=9
+    local statefile="${ZED_RUNDIR}/zed.zedlet.state"
+    local time_now
+    local time_prev
+    local umask_bak
+    local rv=0
+
+    [ -n "${tag}" ] || return 0
+
+    zed_lock "${lockfile}" "${lockfile_fd}"
+    time_now="$(date +%s)"
+    time_prev="$(egrep "^[0-9]+;${tag}\$" "${statefile}" 2>/dev/null \
+        | tail -1 | cut -d\; -f1)"
+
+    if [ -n "${time_prev}" ] \
+            && [ "$((time_now - time_prev))" -lt "${interval}" ]; then
+        rv=1
+    else
+        umask_bak="$(umask)"
+        umask 077
+        egrep -v "^[0-9]+;${tag}\$" "${statefile}" 2>/dev/null \
+            > "${statefile}.$$"
+        echo "${time_now};${tag}" >> "${statefile}.$$"
+        mv -f "${statefile}.$$" "${statefile}"
+        umask "${umask_bak}"
+    fi
+
+    zed_unlock "${lockfile}" "${lockfile_fd}"
+    return "${rv}"
+}