[Libguestfs] [PATCH nbdkit 2/2] log: Add logscript feature.
Richard W.M. Jones
rjones at redhat.com
Sun Dec 20 12:23:08 UTC 2020
This allows you to trigger an external script on log events, instead
(or in addition to) logging to a file.
---
filters/log/nbdkit-log-filter.pod | 113 +++++++++++++++++++++++++++---
filters/log/log.h | 1 +
filters/log/log.c | 60 ++++++++--------
filters/log/output.c | 84 +++++++++++++++++++---
TODO | 4 --
5 files changed, 207 insertions(+), 55 deletions(-)
diff --git a/filters/log/nbdkit-log-filter.pod b/filters/log/nbdkit-log-filter.pod
index abf52e18..dd04f1ab 100644
--- a/filters/log/nbdkit-log-filter.pod
+++ b/filters/log/nbdkit-log-filter.pod
@@ -4,15 +4,24 @@ nbdkit-log-filter - nbdkit log filter
=head1 SYNOPSIS
- nbdkit --filter=log plugin logfile=FILE [logappend=BOOL] [plugin-args...]
+ nbdkit --filter=log PLUGIN
+ [logfile=FILE | logscript=SCRIPT] [logappend=BOOL]
+ [PLUGIN-ARGS...]
=head1 DESCRIPTION
-C<nbdkit-log-filter> is a filter that logs all transactions to a file.
+C<nbdkit-log-filter> is a filter that logs all transactions to a file
+or external script.
+
When used as the first filter, it can show the original client
requests. As a later filter, it can show how earlier filters have
-modified the original request. The format of the log file is
-described in L</LOG FILE FORMAT> below.
+modified the original request.
+
+When using C<logfile=FILE>, logs are written to a log file with the
+format described in L</LOG FILE FORMAT> below.
+
+When using C<logscript=SCRIPT>, logs invoke the external script. See
+L</LOG SCRIPT> below.
An alternative to this filter is simply to run nbdkit with the I<-f>
and I<-v> flags which enable verbose debugging to stderr. This logs
@@ -22,11 +31,20 @@ parsable format and works when nbdkit runs in the background.
=head1 PARAMETERS
+C<logfile> or C<logscript> or both can be given. If neither then the
+filter is inactive.
+
=over 4
=item B<logfile=>FILE
-The file where the log is written. This parameter is required.
+The file where the log is written. See L</LOG FILE FORMAT> below.
+
+=item B<logscript=>SCRIPT
+
+(nbdkit E<ge> 1.24)
+
+Log lines invoke an external script. See L</LOG SCRIPT> below.
=item B<logappend=true>
@@ -34,9 +52,9 @@ The file where the log is written. This parameter is required.
(nbdkit E<ge> 1.8)
-When set to C<false> (the default), if the file already exists it will
-be truncated. When set to C<true>, the filter appends to the existing
-file.
+This only affects C<logfile>. If C<false> (the default), if the file
+already exists it will be truncated. If C<true>, the filter appends
+to the existing log file.
=back
@@ -84,6 +102,85 @@ unique per connection.
Strings and lists are shell-quoted.
+=head1 LOG SCRIPT
+
+If C<logscript=SCRIPT> is given on the command line then log entries
+are passed to the external script.
+
+The script is passed several shell variables:
+
+=over 4
+
+=item C<$act>
+
+The action name, like C<"Read">, C<"Write"> etc.
+
+=item C<$connection>
+
+The connection ID identifying the client, only for connected calls
+like C<"Read">.
+
+=item C<$error>
+
+For messages of type C<"LEAVE"> which fail (C<$return = -1>), this
+contains the errno as a string, for example C<"EIO">.
+
+=item C<$id>
+
+The transaction ID, used to correlate actions which are split into two
+messages C<"ENTER"> and C<"LEAVE">.
+
+=item C<$return>
+
+For messages of type C<"LEAVE"> this is the return code, usually C<0>
+for success and C<-1> if there was an error.
+
+=item C<$type>
+
+The message type: C<"ENTER">, C<"LEAVE"> or C<"PRINT">.
+
+=item other shell variables
+
+Other parameters like C<offset=N> are turned into shell variables
+C<$offset> etc.
+
+=back
+
+Note the return value of the script is ignored. Log scripts cannot
+modify or interrupt request processing.
+
+=head2 Log script examples
+
+The script:
+
+ nbdkit -f --filter=log null 10M \
+ logscript='echo $connection $type $id $act $offset >&2'
+
+might print lines like:
+
+ PRINT Ready
+ 1 ENTER 1 Read 0x0
+ 1 ENTER 2 Write 0x200
+ 1 LEAVE 2 Write
+ 1 LEAVE 1 Read
+
+corresponding to log file lines:
+
+ Ready thread_model=3
+ connection=1 Read id=1 offset=0x0 count=0x200 ...
+ connection=1 Write id=2 offset=0x200 count=0x200 ...
+ connection=1 ...Write id=2
+ connection=1 ...Read id=1
+
+This script will trigger a message when any client reads:
+
+ nbdkit -f --filter=log memory 10M \
+ logscript='
+ if [ "$act" = "Read" -a "$type" = "ENTER" ]; then
+ echo Client is reading $count bytes from $offset >&2
+ fi
+ '
+
=head1 FILES
=over 4
diff --git a/filters/log/log.h b/filters/log/log.h
index 8df27192..6dad10d4 100644
--- a/filters/log/log.h
+++ b/filters/log/log.h
@@ -50,6 +50,7 @@ struct handle {
extern uint64_t connections;
extern const char *logfilename;
extern FILE *logfile;
+extern const char *logscript;
extern int append;
extern pthread_mutex_t lock;
diff --git a/filters/log/log.c b/filters/log/log.c
index 37b36498..7b81a8f1 100644
--- a/filters/log/log.c
+++ b/filters/log/log.c
@@ -62,6 +62,7 @@
uint64_t connections;
const char *logfilename;
FILE *logfile;
+const char *logscript;
int append;
pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
pid_t saved_pid;
@@ -88,23 +89,17 @@ log_config (nbdkit_next_config *next, void *nxdata,
return -1;
return 0;
}
+ if (strcmp (key, "logscript") == 0) {
+ logscript = value;
+ return 0;
+ }
return next (nxdata, key, value);
}
-static int
-log_config_complete (nbdkit_next_config_complete *next, void *nxdata)
-{
- if (!logfilename) {
- nbdkit_error ("missing logfile= parameter for the log filter");
- return -1;
- }
-
- return next (nxdata);
-}
-
#define log_config_help \
- "logfile=<FILE> (required) The file to place the log in.\n" \
- "logappend=<BOOL> True to append to the log (default false).\n"
+ "logfile=<FILE> The file to place the log in.\n" \
+ "logappend=<BOOL> True to append to the log (default false).\n" \
+ "logscript=<SCRIPT> Script to run for logging."
/* Open the logfile. */
static int
@@ -112,24 +107,26 @@ log_get_ready (nbdkit_next_get_ready *next, void *nxdata, int thread_model)
{
int fd;
- /* Using fopen("ae"/"we") would be more convenient, but as Haiku
- * still lacks that, use this instead. Atomicity is not essential
- * here since .config completes before threads that might fork, if
- * we have to later add yet another fallback to fcntl(fileno()) for
- * systems without O_CLOEXEC.
- */
- fd = open (logfilename,
- O_CLOEXEC | O_WRONLY | O_CREAT | (append ? O_APPEND : O_TRUNC),
- 0666);
- if (fd < 0) {
- nbdkit_error ("open: %s: %m", logfilename);
- return -1;
- }
- logfile = fdopen (fd, append ? "a" : "w");
- if (!logfile) {
- nbdkit_error ("fdopen: %s: %m", logfilename);
- close (fd);
- return -1;
+ if (logfilename) {
+ /* Using fopen("ae"/"we") would be more convenient, but as Haiku
+ * still lacks that, use this instead. Atomicity is not essential
+ * here since .config completes before threads that might fork, if
+ * we have to later add yet another fallback to fcntl(fileno()) for
+ * systems without O_CLOEXEC.
+ */
+ fd = open (logfilename,
+ O_CLOEXEC | O_WRONLY | O_CREAT | (append ? O_APPEND : O_TRUNC),
+ 0666);
+ if (fd < 0) {
+ nbdkit_error ("open: %s: %m", logfilename);
+ return -1;
+ }
+ logfile = fdopen (fd, append ? "a" : "w");
+ if (!logfile) {
+ nbdkit_error ("fdopen: %s: %m", logfilename);
+ close (fd);
+ return -1;
+ }
}
saved_pid = getpid ();
@@ -450,7 +447,6 @@ static struct nbdkit_filter filter = {
.name = "log",
.longname = "nbdkit log filter",
.config = log_config,
- .config_complete = log_config_complete,
.config_help = log_config_help,
.unload = log_unload,
.get_ready = log_get_ready,
diff --git a/filters/log/output.c b/filters/log/output.c
index 0bfcf7c8..c999150a 100644
--- a/filters/log/output.c
+++ b/filters/log/output.c
@@ -55,9 +55,10 @@
enum type { ENTER, LEAVE, PRINT };
+/* Adds an entry to the logfile. */
static void
-output (struct handle *h, log_id_t id, const char *act, enum type type,
- const char *fmt, va_list args)
+to_file (struct handle *h, log_id_t id, const char *act, enum type type,
+ const char *fmt, va_list args)
{
struct timeval tv;
struct tm tm;
@@ -103,15 +104,62 @@ output (struct handle *h, log_id_t id, const char *act, enum type type,
#endif
}
+/* Runs the script. */
+static void
+to_script (struct handle *h, log_id_t id, const char *act, enum type type,
+ const char *fmt, va_list args)
+{
+ FILE *fp;
+ CLEANUP_FREE char *str = NULL;
+ size_t len = 0;
+ int r;
+
+ /* Create the shell variables + script. */
+ fp = open_memstream (&str, &len);
+ if (!fp) {
+ /* Not much we can do, but at least record the error. */
+ nbdkit_error ("logscript: open_memstream: %m");
+ return;
+ }
+
+ fprintf (fp, "act=%s\n", act);
+ if (h)
+ fprintf (fp, "connection=%" PRIu64 "\n", h->connection);
+ switch (type) {
+ case ENTER: fprintf (fp, "type=ENTER\n"); break;
+ case LEAVE: fprintf (fp, "type=LEAVE\n"); break;
+ case PRINT: fprintf (fp, "type=PRINT\n"); break;
+ }
+ if (id)
+ fprintf (fp, "id=%" PRIu64 "\n", id);
+
+ vfprintf (fp, fmt, args);
+ fprintf (fp, "\n");
+
+ fprintf (fp, "%s", logscript);
+ fclose (fp);
+
+ /* Run the script. Log the status, but ignore it. */
+ r = system (str);
+ exit_status_to_nbd_error (r, "logscript");
+}
+
void
enter (struct handle *h, log_id_t id, const char *act,
const char *fmt, ...)
{
va_list args;
- va_start (args, fmt);
- output (h, id, act, ENTER, fmt, args);
- va_end (args);
+ if (logfile) {
+ va_start (args, fmt);
+ to_file (h, id, act, ENTER, fmt, args);
+ va_end (args);
+ }
+ if (logscript) {
+ va_start (args, fmt);
+ to_script (h, id, act, ENTER, fmt, args);
+ va_end (args);
+ }
}
void
@@ -120,9 +168,16 @@ leave (struct handle *h, log_id_t id, const char *act,
{
va_list args;
- va_start (args, fmt);
- output (h, id, act, LEAVE, fmt, args);
- va_end (args);
+ if (logfile) {
+ va_start (args, fmt);
+ to_file (h, id, act, LEAVE, fmt, args);
+ va_end (args);
+ }
+ if (logscript) {
+ va_start (args, fmt);
+ to_script (h, id, act, LEAVE, fmt, args);
+ va_end (args);
+ }
}
void
@@ -130,9 +185,16 @@ print (struct handle *h, const char *act, const char *fmt, ...)
{
va_list args;
- va_start (args, fmt);
- output (h, 0, act, PRINT, fmt, args);
- va_end (args);
+ if (logfile) {
+ va_start (args, fmt);
+ to_file (h, 0, act, PRINT, fmt, args);
+ va_end (args);
+ }
+ if (logscript) {
+ va_start (args, fmt);
+ to_script (h, 0, act, PRINT, fmt, args);
+ va_end (args);
+ }
}
void
diff --git a/TODO b/TODO
index cc7afab8..198939e6 100644
--- a/TODO
+++ b/TODO
@@ -202,10 +202,6 @@ Suggestions for filters
* masking plugin features for testing clients (see 'nozero' and 'fua'
filters for examples)
-* "event" filter which triggers shell scripts on significant events
- (like connection, close, read, write, etc). It would not modify the
- requests but allow more flexible logging.
-
* "bandwidth quota" filter which would close a connection after it
exceeded a certain amount of bandwidth up or down.
--
2.29.0.rc2
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