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 <[email protected]>
Reviewed-by: Matt Ahrens <[email protected]>
Reviewed-by: Igor Kozhukhov <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Chunwei Chen <[email protected]>
Closes #9516 

1 files changed, 11 insertions, 9 deletions

diff --git a/lib/libzfs/libzfs_pool.c b/lib/libzfs/libzfs_pool.c
index 75ce7c9ab..380229da5 100644
--- a/lib/libzfs/libzfs_pool.c
+++ b/lib/libzfs/libzfs_pool.c
@@ -4160,33 +4160,37 @@ get_history(zpool_handle_t *zhp, char *buf, uint64_t *off, uint64_t *len)
  * 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;
 	int buflen = 128 * 1024;
-	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 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)
+		if (!bytes_read) {
+			*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
@@ -4198,9 +4202,7 @@ zpool_get_history(zpool_handle_t *zhp, nvlist_t **nvhisp)
 			if (buf == NULL)
 				return (ENOMEM);
 		}
-
-		/* CONSTCOND */
-	} while (1);
+	}
 
 	free(buf);