cachedel: remove file from fs cache

Makefile

 default:
 	gcc -Wall -o cachestats cachestats.c
+	gcc -Wall -o cachedel cachedel.c
 	gcc -Wall -fPIC -c -o nocache.o nocache.c
 	gcc -Wall -fPIC -c -o fcntl_helpers.o fcntl_helpers.c
 	gcc -Wall -shared -Wl,-soname,nocache.so.1 -ldl -o nocache.so nocache.o fcntl_helpers.o

cachedel.c

+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <error.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+int exiterr(const char *s)
+{
+    perror(s);
+    exit(-1);
+}
+
+int main(int argc, char *argv[])
+{
+    int fd;
+    struct stat st;
+
+    if(argc != 2) {
+        fprintf(stderr, "usage: %s <file> "
+            "-- call fadvise(DONTNEED) on file", argv[0]);
+        exit(1);
+    }
+
+    fd = open(argv[1], 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]);
+        return EXIT_FAILURE;
+    }
+    if(st.st_size == 0) {
+        fprintf(stderr, "%s: file size is 0!\n", argv[1]);
+        return EXIT_FAILURE;
+    }
+
+    if(posix_fadvise(fd, 0, 0, POSIX_FADV_DONTNEED) == -1)
+        exiterr("posix_fadvise");
+
+    return EXIT_SUCCESS;
+}