Implement "-n <n>" flag for repeated posix_fadvise()

cachedel.c

@@ -4,6 +4,7 @@
 #include <error.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 
 int exiterr(const char *s)
 {
@@ -13,30 +14,38 @@ int exiterr(const char *s)
 
 int main(int argc, char *argv[])
 {
+    int i, n = 1;
     int fd;
+    char *fn;
     struct stat st;
 
-    if(argc != 2) {
-        fprintf(stderr, "usage: %s <file> "
-            "-- call fadvise(DONTNEED) on file", argv[0]);
+    if(argc == 4 && !strcmp("-n", argv[1])) {
+            n = atoi(argv[2]);
+            fn = argv[3];
+    } else if(argc != 2) {
+        fprintf(stderr, "usage: %s [-n <n>] <file> "
+            "-- call fadvise(DONTNEED) <n> times on file", argv[0]);
         exit(1);
+    } else {
+        fn = argv[1];
     }
 
-    fd = open(argv[1], O_RDONLY);
+    fd = open(fn, O_RDONLY);
     if(fd == -1)
         exiterr("open");
 
     if(fstat(fd, &st) == -1)
         exiterr("fstat");
     if(!S_ISREG(st.st_mode)) {
-        fprintf(stderr, "%s: S_ISREG: not a regular file", argv[1]);
+        fprintf(stderr, "%s: S_ISREG: not a regular file", fn);
         return EXIT_FAILURE;
     }
     if(st.st_size == 0) {
-        fprintf(stderr, "%s: file size is 0!\n", argv[1]);
+        fprintf(stderr, "%s: file size is 0!\n", fn);
         return EXIT_FAILURE;
     }
 
+    for(i = 0; i < n; i++)
         if(posix_fadvise(fd, 0, 0, POSIX_FADV_DONTNEED) == -1)
             exiterr("posix_fadvise");
 

fcntl_helpers.c

@@ -5,12 +5,12 @@
 /* Since open() and close() are re-defined in nocache.c, it's not
  * possible to include <fcntl.h> there. So we do it here. */
 
-int fadv_dontneed(int fd, off_t offset, off_t len)
+int fadv_dontneed(int fd, off_t offset, off_t len, int n)
 {
-#ifdef DOUBLEFADVISE
-        posix_fadvise(fd, offset, len, POSIX_FADV_DONTNEED);
-#endif
-        return posix_fadvise(fd, offset, len, POSIX_FADV_DONTNEED);
+        int i, ret;
+        for(i = 0; i < n; i++)
+            ret = posix_fadvise(fd, offset, len, POSIX_FADV_DONTNEED);
+        return ret;
 }
 
 int fadv_noreuse(int fd, off_t offset, off_t len)

fcntl_helpers.h

 #ifndef _FCNTL_HELPERS_H
 #define _FCNTL_HELPERS_H
-extern int fadv_dontneed(int fd, off_t offset, off_t len);
+extern int fadv_dontneed(int fd, off_t offset, off_t len, int n);
 extern int fadv_noreuse(int fd, off_t offset, off_t len);
 extern int valid_fd(int fd);
 extern void sync_if_writable(int fd);

nocache

@@ -8,4 +8,9 @@ else
     export LD_PRELOAD="$libnocache"
 fi
 
+if [ "$1" = "-n" ]; then
+    export NOCACHE_NR_FADVISE="$2"
+    shift 2
+fi
+
 exec "$@"

nocache.c

@@ -60,9 +60,13 @@ static struct fadv_info fds[_MAX_FDS];
 static size_t PAGESIZE;
 static pthread_mutex_t lock; /* protects access to fds[] */
 
+static char *env_nr_fadvise = "NOCACHE_NR_FADVISE";
+static int nr_fadvise;
+
 static void init(void)
 {
     int i;
+    char *s;
     char *error;
 
     _original_open = (int (*)(const char *, int, mode_t))
@@ -82,6 +86,11 @@ static void init(void)
         exit(EXIT_FAILURE);
     }
 
+    if((s = getenv(env_nr_fadvise)) != NULL)
+        nr_fadvise = atoi(s);
+    if(nr_fadvise <= 0)
+        nr_fadvise = 1;
+
     PAGESIZE = getpagesize();
     for(i = 0; i < _MAX_FDS; i++)
         fds[i].fd = -1;
@@ -295,14 +304,14 @@ static void free_unclaimed_pages(int fd)
     while(j < fds[i].nr_pages) {
         if(fds[i].info[j] & 1) {
             if(start < j)
-                fadv_dontneed(fd, start*PAGESIZE, (j - start) * PAGESIZE);
+                fadv_dontneed(fd, start*PAGESIZE, (j - start) * PAGESIZE, nr_fadvise);
             start = j + 1;
         }
         j++;
     }
 
     /* forget written contents that go beyond previous file size */
-    fadv_dontneed(fd, start < j ? start*PAGESIZE : fds[i].size, 0);
+    fadv_dontneed(fd, start < j ? start*PAGESIZE : fds[i].size, 0, nr_fadvise);
 
     free(fds[i].info);
     fds[i].fd = -1;