8677 Open-Context Channel Programs

Reviewed by: Matt Ahrens <mahrens@delphix.com>
Reviewed by: Chris Williamson <chris.williamson@delphix.com>
Reviewed by: Pavel Zakharov <pavel.zakharov@delphix.com>

We want to be able to run channel programs outside of synching context.
This would greatly improve performance for channel programs that just gather
information, as they won't have to wait for synching context anymore.

=== What is implemented?

This feature introduces the following:
- A new command line flag in "zfs program" to specify our intention
  to run in open context. (The -n option)
- A new flag/option within the channel program ioctl which selects
  the context.
- Appropriate error handling whenever we try a channel program in
  open-context that contains zfs.sync* expressions.
- Documentation for the new feature in the manual pages.

=== How do we handle zfs.sync functions in open context?

When such a function is found by the interpreter and we are running
in open context we abort the script and we spit out a descriptive
runtime error. For example, given the script below ...

arg = ...
fs = arg["argv"][1]
err = zfs.sync.destroy(fs)
msg = "destroying " .. fs .. " err=" .. err
return msg

if we run it in open context, we will get back the following error:

Channel program execution failed:
[string "channel program"]:3: running functions from the zfs.sync submodule requires passing sync=TRUE to lzc_channel_program() (i.e. do not specify the "-n" command line argument)
stack traceback:
        [C]: in function 'destroy'
        [string "channel program"]:3: in main chunk

=== What about testing?

We've introduced new wrappers for all channel program tests that
run each channel program as both (startard & open-context) and
expect the appropriate behavior depending on the program using
the zfs.sync module.

Closes #469

usr/src/cmd/zfs/zfs_main.c

@@ -329,7 +329,7 @@ get_usage(zfs_help_t idx)
 	case HELP_BOOKMARK:
 		return (gettext("\tbookmark <snapshot> <bookmark>\n"));
 	case HELP_CHANNEL_PROGRAM:
-		return (gettext("\tprogram [-t <instruction limit>] "
+		return (gettext("\tprogram [-n] [-t <instruction limit>] "
 		    "[-m <memory limit (b)>] <pool> <program file> "
 		    "[lua args...]\n"));
 	}
@@ -7009,11 +7009,12 @@ zfs_do_channel_program(int argc, char **argv)
 	nvlist_t *outnvl;
 	uint64_t instrlimit = ZCP_DEFAULT_INSTRLIMIT;
 	uint64_t memlimit = ZCP_DEFAULT_MEMLIMIT;
+	boolean_t sync_flag = B_TRUE;
 	zpool_handle_t *zhp;
 
 	/* check options */
 	while (-1 !=
-	    (c = getopt(argc, argv, "t:(instr-limit)m:(memory-limit)"))) {
+	    (c = getopt(argc, argv, "nt:(instr-limit)m:(memory-limit)"))) {
 		switch (c) {
 		case 't':
 		case 'm': {
@@ -7051,6 +7052,10 @@ zfs_do_channel_program(int argc, char **argv)
 			}
 			break;
 		}
+		case 'n': {
+			sync_flag = B_FALSE;
+			break;
+		}
 		case '?':
 			(void) fprintf(stderr, gettext("invalid option '%c'\n"),
 			    optopt);
@@ -7122,8 +7127,13 @@ zfs_do_channel_program(int argc, char **argv)
 	nvlist_t *argnvl = fnvlist_alloc();
 	fnvlist_add_string_array(argnvl, ZCP_ARG_CLIARGV, argv + 2, argc - 2);
 
-	ret = lzc_channel_program(poolname, progbuf, instrlimit, memlimit,
-	    argnvl, &outnvl);
+	if (sync_flag) {
+		ret = lzc_channel_program(poolname, progbuf,
+		    instrlimit, memlimit, argnvl, &outnvl);
+	} else {
+		ret = lzc_channel_program_nosync(poolname, progbuf,
+		    instrlimit, memlimit, argnvl, &outnvl);
+	}
 
 	if (ret != 0) {
 		/*

usr/src/lib/libzfs/common/libzfs_dataset.c

@@ -2348,7 +2348,7 @@ zcp_check(zfs_handle_t *zhp, zfs_prop_t prop, uint64_t intval,
 	fnvlist_add_string(argnvl, "dataset", zhp->zfs_name);
 	fnvlist_add_string(argnvl, "property", zfs_prop_to_name(prop));
 
-	error = lzc_channel_program(poolname, program,
+	error = lzc_channel_program_nosync(poolname, program,
 	    10 * 1000 * 1000, 10 * 1024 * 1024, argnvl, &outnvl);
 
 	if (error == 0) {

usr/src/lib/libzfs_core/common/libzfs_core.c

@@ -881,6 +881,25 @@ lzc_destroy_bookmarks(nvlist_t *bmarks, nvlist_t **errlist)
 	return (error);
 }
 
+static int
+lzc_channel_program_impl(const char *pool, const char *program, boolean_t sync,
+    uint64_t instrlimit, uint64_t memlimit, nvlist_t *argnvl, nvlist_t **outnvl)
+{
+	int error;
+	nvlist_t *args;
+
+	args = fnvlist_alloc();
+	fnvlist_add_string(args, ZCP_ARG_PROGRAM, program);
+	fnvlist_add_nvlist(args, ZCP_ARG_ARGLIST, argnvl);
+	fnvlist_add_boolean_value(args, ZCP_ARG_SYNC, sync);
+	fnvlist_add_uint64(args, ZCP_ARG_INSTRLIMIT, instrlimit);
+	fnvlist_add_uint64(args, ZCP_ARG_MEMLIMIT, memlimit);
+	error = lzc_ioctl(ZFS_IOC_CHANNEL_PROGRAM, pool, args, outnvl);
+	fnvlist_free(args);
+
+	return (error);
+}
+
 /*
  * Executes a channel program.
  *
@@ -918,16 +937,26 @@ int
 lzc_channel_program(const char *pool, const char *program, uint64_t instrlimit,
     uint64_t memlimit, nvlist_t *argnvl, nvlist_t **outnvl)
 {
-	int error;
-	nvlist_t *args;
-
-	args = fnvlist_alloc();
-	fnvlist_add_string(args, ZCP_ARG_PROGRAM, program);
-	fnvlist_add_nvlist(args, ZCP_ARG_ARGLIST, argnvl);
-	fnvlist_add_uint64(args, ZCP_ARG_INSTRLIMIT, instrlimit);
-	fnvlist_add_uint64(args, ZCP_ARG_MEMLIMIT, memlimit);
-	error = lzc_ioctl(ZFS_IOC_CHANNEL_PROGRAM, pool, args, outnvl);
-	fnvlist_free(args);
+	return (lzc_channel_program_impl(pool, program, B_TRUE, instrlimit,
+	    memlimit, argnvl, outnvl));
+}
 
-	return (error);
+/*
+ * Executes a read-only channel program.
+ *
+ * A read-only channel program works programmatically the same way as a
+ * normal channel program executed with lzc_channel_program(). The only
+ * difference is it runs exclusively in open-context and therefore can
+ * return faster. The downside to that, is that the program cannot change
+ * on-disk state by calling functions from the zfs.sync submodule.
+ *
+ * The return values of this function (and their meaning) are exactly the
+ * same as the ones described in lzc_channel_program().
+ */
+int
+lzc_channel_program_nosync(const char *pool, const char *program,
+    uint64_t timeout, uint64_t memlimit, nvlist_t *argnvl, nvlist_t **outnvl)
+{
+	return (lzc_channel_program_impl(pool, program, B_FALSE, timeout,
+	    memlimit, argnvl, outnvl));
 }

usr/src/lib/libzfs_core/common/libzfs_core.h

@@ -86,8 +86,10 @@ boolean_t lzc_exists(const char *);
 int lzc_rollback(const char *, char *, int);
 int lzc_rollback_to(const char *, const char *);
 
-int lzc_channel_program(const char *, const char *, uint64_t, uint64_t,
-    nvlist_t *, nvlist_t **);
+int lzc_channel_program(const char *, const char *, uint64_t,
+    uint64_t, nvlist_t *, nvlist_t **);
+int lzc_channel_program_nosync(const char *, const char *, uint64_t,
+    uint64_t, nvlist_t *, nvlist_t **);
 
 #ifdef	__cplusplus
 }

usr/src/lib/libzfs_core/common/mapfile-vers

@@ -44,6 +44,7 @@ SYMBOL_VERSION ILLUMOS_0.1 {
 	libzfs_core_init;
 	lzc_bookmark;
 	lzc_channel_program;
+	lzc_channel_program_nosync;
 	lzc_clone;
 	lzc_promote;
 	lzc_create;

usr/src/man/man1m/zfs-program.1m

@@ -18,6 +18,7 @@
 .Nd executes ZFS channel programs
 .Sh SYNOPSIS
 .Cm "zfs program"
+.Op Fl n
 .Op Fl t Ar instruction-limit
 .Op Fl m Ar memory-limit
 .Ar pool
@@ -45,6 +46,14 @@ will be run on
 and any attempts to access or modify other pools will cause an error.
 .Sh OPTIONS
 .Bl -tag -width "-t"
+.It Fl n
+Executes a read-only channel program, which runs faster.
+The program cannot change on-disk state by calling functions from the
+zfs.sync submodule.
+The program can be used to gather information such as properties and
+determining if changes would succeed (zfs.check.*).
+Without this flag, all pending changes must be synced to disk before a
+channel program can complete.
 .It Fl t Ar instruction-limit
 Execution time limit, in number of Lua instructions to execute.
 If a channel program executes more than the specified number of instructions,

usr/src/man/man1m/zfs.1m

@@ -267,6 +267,7 @@
 .Ar snapshot Ar snapshot Ns | Ns Ar filesystem
 .Nm
 .Cm program
+.Op Fl n
 .Op Fl t Ar timeout
 .Op Fl m Ar memory_limit
 .Ar pool script
@@ -3408,6 +3409,7 @@ Display the path's inode change time as the first column of output.
 .It Xo
 .Nm
 .Cm program
+.Op Fl n
 .Op Fl t Ar timeout
 .Op Fl m Ar memory_limit
 .Ar pool script
@@ -3427,8 +3429,15 @@ Channel programs may only be run with root privileges.
 .sp
 For full documentation of the ZFS channel program interface, see the manual
 page for
-.Xr zfs-program 1M .
 .Bl -tag -width ""
+.It Fl n
+Executes a read-only channel program, which runs faster.
+The program cannot change on-disk state by calling functions from
+the zfs.sync submodule.
+The program can be used to gather information such as properties and
+determining if changes would succeed (zfs.check.*).
+Without this flag, all pending changes must be synced to disk before
+a channel program can complete.
 .It Fl t Ar timeout
 Execution time limit, in milliseconds.
 If a channel program executes for longer than the provided timeout, it will