MFOpenZFS: Fix zpool history unbounded memory usage

In original implementation, zpool history will read the whole history
before printing anything, causing memory usage goes unbounded. We fix
this by breaking it into read-print iterations.

Reviewed-by: Tom Caputi <tcaputi@datto.com>
Reviewed-by: Matt Ahrens <matt@delphix.com>
Reviewed-by: Igor Kozhukhov <igor@dilos.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Chunwei Chen <david.chen@nutanix.com>
Closes #9516

Note, this change changes the libzfs.so ABI by modifying the prototype
of zpool_get_history().  Since libzfs is effectively private to the base
system it is anticipated that this will not be a problem.

PR:		247557
Obtained from:	OpenZFS
Reported and tested by:	Sam Vaughan <samjvaughan@gmail.com>
Discussed with:	freqlabs
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D25745
openzfs/zfs@7125a109dcc55628336ff3f58e59e503f4d7694d

3 files changed, 41 insertions, 26 deletions

diff --git a/cddl/contrib/opensolaris/cmd/zpool/zpool_main.c b/cddl/contrib/opensolaris/cmd/zpool/zpool_main.c
index 414f26756acd0..35c3db7893df4 100644
--- a/cddl/contrib/opensolaris/cmd/zpool/zpool_main.c
+++ b/cddl/contrib/opensolaris/cmd/zpool/zpool_main.c
@@ -6226,24 +6226,12 @@ typedef struct hist_cbdata {
 	boolean_t internal;
 } hist_cbdata_t;
 
-/*
- * Print out the command history for a specific pool.
- */
-static int
-get_history_one(zpool_handle_t *zhp, void *data)
+static void
+print_history_records(nvlist_t *nvhis, hist_cbdata_t *cb)
 {
-	nvlist_t *nvhis;
 	nvlist_t **records;
 	uint_t numrecords;
-	int ret, i;
-	hist_cbdata_t *cb = (hist_cbdata_t *)data;
-
-	cb->first = B_FALSE;
-
-	(void) printf(gettext("History for '%s':\n"), zpool_get_name(zhp));
-
-	if ((ret = zpool_get_history(zhp, &nvhis)) != 0)
-		return (ret);
+	int i;
 
 	verify(nvlist_lookup_nvlist_array(nvhis, ZPOOL_HIST_RECORD,
 	    &records, &numrecords) == 0);
@@ -6344,8 +6332,32 @@ get_history_one(zpool_handle_t *zhp, void *data)
 		(void) printf("]");
 		(void) printf("\n");
 	}
+}
+
+/*
+ * Print out the command history for a specific pool.
+ */
+static int
+get_history_one(zpool_handle_t *zhp, void *data)
+{
+	nvlist_t *nvhis;
+	int ret;
+	hist_cbdata_t *cb = (hist_cbdata_t *)data;
+	uint64_t off = 0;
+	boolean_t eof = B_FALSE;
+
+	cb->first = B_FALSE;
+
+	(void) printf(gettext("History for '%s':\n"), zpool_get_name(zhp));
+
+	while (!eof) {
+		if ((ret = zpool_get_history(zhp, &nvhis, &off, &eof)) != 0)
+			return (ret);
+
+		print_history_records(nvhis, cb);
+		nvlist_free(nvhis);
+	}
 	(void) printf("\n");
-	nvlist_free(nvhis);
 
 	return (ret);
 }
diff --git a/cddl/contrib/opensolaris/lib/libzfs/common/libzfs.h b/cddl/contrib/opensolaris/lib/libzfs/common/libzfs.h
index 7be49cb7e4e09..469d61f5e773c 100644
--- a/cddl/contrib/opensolaris/lib/libzfs/common/libzfs.h
+++ b/cddl/contrib/opensolaris/lib/libzfs/common/libzfs.h
@@ -441,7 +441,8 @@ typedef enum {
 extern char *zpool_vdev_name(libzfs_handle_t *, zpool_handle_t *, nvlist_t *,
     int name_flags);
 extern int zpool_upgrade(zpool_handle_t *, uint64_t);
-extern int zpool_get_history(zpool_handle_t *, nvlist_t **);
+extern int zpool_get_history(zpool_handle_t *, nvlist_t **, uint64_t *,
+    boolean_t *);
 extern int zpool_history_unpack(char *, uint64_t, uint64_t *,
     nvlist_t ***, uint_t *);
 extern void zpool_obj_to_path(zpool_handle_t *, uint64_t, uint64_t, char *,
diff --git a/cddl/contrib/opensolaris/lib/libzfs/common/libzfs_pool.c b/cddl/contrib/opensolaris/lib/libzfs/common/libzfs_pool.c
index c2dac2362f10a..39b6c35f6fbd0 100644
--- a/cddl/contrib/opensolaris/lib/libzfs/common/libzfs_pool.c
+++ b/cddl/contrib/opensolaris/lib/libzfs/common/libzfs_pool.c
@@ -4124,33 +4124,37 @@ zpool_history_unpack(char *buf, uint64_t bytes_read, uint64_t *leftover,
  * Retrieve the command history of a pool.
  */
 int
-zpool_get_history(zpool_handle_t *zhp, nvlist_t **nvhisp)
+zpool_get_history(zpool_handle_t *zhp, nvlist_t **nvhisp, uint64_t *off,
+    boolean_t *eof)
 {
 	char *buf;
 	uint64_t buflen = HIS_BUF_LEN_DEF;
-	uint64_t off = 0;
 	nvlist_t **records = NULL;
 	uint_t numrecords = 0;
 	int err, i;
+	uint64_t start = *off;
 
 	buf = malloc(buflen);
 	if (buf == NULL)
 		return (ENOMEM);
-	do {
+	/* process about 1MB at a time */
+	while (*off - start < 1024 * 1024) {
 		uint64_t bytes_read = buflen;
 		uint64_t leftover;
 
-		if ((err = get_history(zhp, buf, &off, &bytes_read)) != 0)
+		if ((err = get_history(zhp, buf, off, &bytes_read)) != 0)
 			break;
 
 		/* if nothing else was read in, we're at EOF, just return */
-		if (bytes_read == 0)
+		if (bytes_read == 0) {
+			*eof = B_TRUE;
 			break;
+		}
 
 		if ((err = zpool_history_unpack(buf, bytes_read,
 		    &leftover, &records, &numrecords)) != 0)
 			break;
-		off -= leftover;
+		*off -= leftover;
 		if (leftover == bytes_read) {
 			/*
 			 * no progress made, because buffer is not big enough
@@ -4165,9 +4169,7 @@ zpool_get_history(zpool_handle_t *zhp, nvlist_t **nvhisp)
 				break;
 			}
 		}
-
-		/* CONSTCOND */
-	} while (1);
+	}
 
 	free(buf);