Extend the VMM stats interface to support a dynamic count of statistics.

- Add a starting index to 'struct vmstats' and change the
  VM_STATS ioctl to fetch the 64 stats starting at that index.
  A compat shim for <= 13 continues to fetch only the first 64
  stats.

- Extend vm_get_stats() in libvmmapi to use a loop and a static
  thread local buffer which grows to hold the stats needed.

Reviewed by:	markj
Differential Revision:	https://reviews.freebsd.org/D27463

1 files changed, 33 insertions, 8 deletions

diff --git a/lib/libvmmapi/vmmapi.c b/lib/libvmmapi/vmmapi.c
index a2d26b1b33b9..0291e4a10c33 100644
--- a/lib/libvmmapi/vmmapi.c
+++ b/lib/libvmmapi/vmmapi.c
@@ -1066,19 +1066,44 @@ uint64_t *
 vm_get_stats(struct vmctx *ctx, int vcpu, struct timeval *ret_tv,
 	     int *ret_entries)
 {
-	int error;
-
-	static struct vm_stats vmstats;
-
+	static _Thread_local uint64_t *stats_buf;
+	static _Thread_local u_int stats_count;
+	uint64_t *new_stats;
+	struct vm_stats vmstats;
+	u_int count, index;
+	bool have_stats;
+
+	have_stats = false;
 	vmstats.cpuid = vcpu;
+	count = 0;
+	for (index = 0;; index += nitems(vmstats.statbuf)) {
+		vmstats.index = index;
+		if (ioctl(ctx->fd, VM_STATS, &vmstats) != 0)
+			break;
+		if (stats_count < index + vmstats.num_entries) {
+			new_stats = realloc(stats_buf,
+			    (index + vmstats.num_entries) * sizeof(uint64_t));
+			if (new_stats == NULL) {
+				errno = ENOMEM;
+				return (NULL);
+			}
+			stats_count = index + vmstats.num_entries;
+			stats_buf = new_stats;
+		}
+		memcpy(stats_buf + index, vmstats.statbuf,
+		    vmstats.num_entries * sizeof(uint64_t));
+		count += vmstats.num_entries;
+		have_stats = true;
 
-	error = ioctl(ctx->fd, VM_STATS, &vmstats);
-	if (error == 0) {
+		if (vmstats.num_entries != nitems(vmstats.statbuf))
+			break;
+	}
+	if (have_stats) {
 		if (ret_entries)
-			*ret_entries = vmstats.num_entries;
+			*ret_entries = count;
 		if (ret_tv)
 			*ret_tv = vmstats.tv;
-		return (vmstats.statbuf);
+		return (stats_buf);
 	} else
 		return (NULL);
 }