Don't race in FreeBSD devstat collector

Querying the number of devices separately from the device list itself is
racy. Devices may be added or removed between the two calls; and removed
devices would lead to a segfault.

1 files changed, 46 insertions, 53 deletions

diff --git a/collector/devstat_freebsd.c b/collector/devstat_freebsd.c
index 3a8e6d3..80a24e4 100644
--- a/collector/devstat_freebsd.c
+++ b/collector/devstat_freebsd.c
@@ -9,66 +9,59 @@
 #include <string.h>
 #include <devstat_freebsd.h>
 
-int _get_ndevs() {
-        struct statinfo current;
-        struct devinfo info = {};
-        current.dinfo = &info;
-
-        devstat_checkversion(NULL);
-
-        if (devstat_getdevs(NULL, &current) == -1)
-                return -1;
 
-        return current.dinfo->numdevs;
-}
-
-Stats _get_stats(int i) {
+int _get_stats(Stats **stats) {
         struct statinfo current;
         struct devinfo info = {};
         current.dinfo = &info;
 
-        devstat_getdevs(NULL, &current);
+        if (devstat_getdevs(NULL, &current) == -1) {
+                return -1;
+        }
 
-        Stats stats;
-        uint64_t bytes_read, bytes_write, bytes_free;
-        uint64_t transfers_other, transfers_read, transfers_write, transfers_free;
-        long double duration_other, duration_read, duration_write, duration_free;
-        long double busy_time;
-        uint64_t blocks;
+        Stats *p = (Stats*)calloc(current.dinfo->numdevs, sizeof(Stats));
+        for (int i = 0; i < current.dinfo->numdevs; i++) {
+                uint64_t bytes_read, bytes_write, bytes_free;
+                uint64_t transfers_other, transfers_read, transfers_write, transfers_free;
+                long double duration_other, duration_read, duration_write, duration_free;
+                long double busy_time;
+                uint64_t blocks;
 
-        strcpy(stats.device, current.dinfo->devices[i].device_name);
-        stats.unit = current.dinfo->devices[i].unit_number;
-        devstat_compute_statistics(&current.dinfo->devices[i],
-                NULL,
-                1.0,
-                DSM_TOTAL_BYTES_READ, &bytes_read,
-                DSM_TOTAL_BYTES_WRITE, &bytes_write,
-                DSM_TOTAL_BYTES_FREE, &bytes_free,
-                DSM_TOTAL_TRANSFERS_OTHER, &transfers_other,
-                DSM_TOTAL_TRANSFERS_READ, &transfers_read,
-                DSM_TOTAL_TRANSFERS_WRITE, &transfers_write,
-                DSM_TOTAL_TRANSFERS_FREE, &transfers_free,
-                DSM_TOTAL_DURATION_OTHER, &duration_other,
-                DSM_TOTAL_DURATION_READ, &duration_read,
-                DSM_TOTAL_DURATION_WRITE, &duration_write,
-                DSM_TOTAL_DURATION_FREE, &duration_free,
-                DSM_TOTAL_BUSY_TIME, &busy_time,
-                DSM_TOTAL_BLOCKS, &blocks,
-                DSM_NONE);
+                strcpy(p[i].device, current.dinfo->devices[i].device_name);
+                p[i].unit = current.dinfo->devices[i].unit_number;
+                devstat_compute_statistics(&current.dinfo->devices[i],
+                                NULL,
+                                1.0,
+                                DSM_TOTAL_BYTES_READ, &bytes_read,
+                                DSM_TOTAL_BYTES_WRITE, &bytes_write,
+                                DSM_TOTAL_BYTES_FREE, &bytes_free,
+                                DSM_TOTAL_TRANSFERS_OTHER, &transfers_other,
+                                DSM_TOTAL_TRANSFERS_READ, &transfers_read,
+                                DSM_TOTAL_TRANSFERS_WRITE, &transfers_write,
+                                DSM_TOTAL_TRANSFERS_FREE, &transfers_free,
+                                DSM_TOTAL_DURATION_OTHER, &duration_other,
+                                DSM_TOTAL_DURATION_READ, &duration_read,
+                                DSM_TOTAL_DURATION_WRITE, &duration_write,
+                                DSM_TOTAL_DURATION_FREE, &duration_free,
+                                DSM_TOTAL_BUSY_TIME, &busy_time,
+                                DSM_TOTAL_BLOCKS, &blocks,
+                                DSM_NONE);
 
-        stats.bytes.read = bytes_read;
-        stats.bytes.write = bytes_write;
-        stats.bytes.free = bytes_free;
-        stats.transfers.other = transfers_other;
-        stats.transfers.read = transfers_read;
-        stats.transfers.write = transfers_write;
-        stats.transfers.free = transfers_free;
-        stats.duration.other = duration_other;
-        stats.duration.read = duration_read;
-        stats.duration.write = duration_write;
-        stats.duration.free = duration_free;
-        stats.busyTime = busy_time;
-        stats.blocks = blocks;
+                p[i].bytes.read = bytes_read;
+                p[i].bytes.write = bytes_write;
+                p[i].bytes.free = bytes_free;
+                p[i].transfers.other = transfers_other;
+                p[i].transfers.read = transfers_read;
+                p[i].transfers.write = transfers_write;
+                p[i].transfers.free = transfers_free;
+                p[i].duration.other = duration_other;
+                p[i].duration.read = duration_read;
+                p[i].duration.write = duration_write;
+                p[i].duration.free = duration_free;
+                p[i].busyTime = busy_time;
+                p[i].blocks = blocks;
+        }
 
-        return stats;
+        *stats = p;
+        return current.dinfo->numdevs;
 }