cache file descriptors

1 files changed, 41 insertions, 21 deletions

diff --git a/watchdog.c b/watchdog.c
index 749b5e4..806fbcc 100644
--- a/watchdog.c
+++ b/watchdog.c
@@ -27,6 +27,7 @@
 struct process
 {
     unsigned int pid;
+    int fd;
     unsigned int time[WATCHDOG_SAMPLES];
 };
 
@@ -36,7 +37,7 @@ struct process_tab
     struct process arr[MAX_PROCESS];
 };
 
-static int pids[MAX_PROCESS];
+static unsigned int pids[MAX_PROCESS];
 static struct process_tab process_tabs[2];
 static char dirbuffer[DIRBUFFER_SIZE];
 static char statbuffer[BUFSIZ];
@@ -90,6 +91,12 @@ int main(int argc, char **argv)
         return EXIT_FAILURE;
     }
 
+    int dirfd = open("/proc", O_RDONLY | O_DIRECTORY);
+    if (dirfd == -1) {
+        perror("open /proc");
+        return EXIT_FAILURE;
+    }
+
     unsigned int times[WATCHDOG_SAMPLES];
     unsigned int num_samples = 0;
     unsigned int bursting_pid = 0;
@@ -106,9 +113,8 @@ int main(int argc, char **argv)
         clock_gettime(CLOCK_BOOTTIME, &ts);
         times[0] = ts.tv_sec * clock_tick + ts.tv_nsec * clock_tick / 1000000000;
 
-        int dirfd = open("/proc", O_RDONLY | O_DIRECTORY);
-        if (dirfd == -1) {
-            perror("open /proc");
+        if (lseek(dirfd, 0, SEEK_SET) != 0) {
+            perror("seek /proc");
             return EXIT_FAILURE;
         }
 
@@ -138,37 +144,48 @@ int main(int argc, char **argv)
         procs->num = 0;
         size_t oldproc_idx = 0;
         for (size_t i = 0; i < num_pids; i++) {
-            char statname[20];
-            snprintf(statname, 20, "%d/stat", pids[i]);
+            struct process *oldproc = NULL;
+            if (num_samples > 1) {
+                while (oldproc_idx < oldprocs->num && oldprocs->arr[oldproc_idx].pid < pids[i]) {
+                    close(oldprocs->arr[oldproc_idx].fd);
+                    oldproc_idx++;
+                }
+                if (oldproc_idx < oldprocs->num && oldprocs->arr[oldproc_idx].pid == pids[i])
+                    oldproc = &oldprocs->arr[oldproc_idx];
+            }
 
-            int statfd = openat(dirfd, statname, O_RDONLY);
-            if (statfd == -1) // fail silently
-                continue;
+            int statfd;
+            if (oldproc) {
+                statfd = oldproc->fd;
+            } else {
+                char statname[20];
+                snprintf(statname, 20, "%d/stat", pids[i]);
 
-            ssize_t n_read = read(statfd, statbuffer, BUFSIZ-1);
+                statfd = openat(dirfd, statname, O_RDONLY);
+                if (statfd == -1) // fail silently
+                    continue;
+            }
+
+            ssize_t n_read = pread(statfd, statbuffer, BUFSIZ-1, 0);
             close(statfd);
-            if (n_read == -1)
+            if (n_read == -1) {
+                close(statfd);
                 continue;
+            }
             statbuffer[n_read] = '\0';
 
             char *name = nth_word(1, statbuffer, n_read+1);
             char *utime = nth_word(13, statbuffer, n_read+1);
             char *stime = nth_word(14, statbuffer, n_read+1);
-            if (!name || !utime || !stime)
+            if (!name || !utime || !stime) {
+                close(statfd);
                 continue;
+            }
 
             struct process *proc = &procs->arr[procs->num++];
             proc->pid = pids[i];
             proc->time[0] = atoi(utime) + atoi(stime);
 
-            struct process *oldproc = NULL;
-            if (num_samples > 1) {
-                while (oldproc_idx < oldprocs->num && oldprocs->arr[oldproc_idx].pid < proc->pid)
-                    oldproc_idx++;
-                if (oldproc_idx < oldprocs->num && oldprocs->arr[oldproc_idx].pid == proc->pid)
-                    oldproc = &oldprocs->arr[oldproc_idx];
-            }
-
             if (oldproc) {
                 memcpy(&proc->time[1], &oldproc->time[0], (WATCHDOG_SAMPLES-1) * sizeof(int));
             } else {
@@ -200,7 +217,10 @@ int main(int argc, char **argv)
             }
         }
 
-        close(dirfd);
+        while (oldproc_idx < oldprocs->num) {
+            close(oldprocs->arr[oldproc_idx].fd);
+            oldproc_idx++;
+        }
 
         struct process_tab *tmp = oldprocs;
         oldprocs = procs;