fallocate: code optimalizations

Based on Pádraig Brady review:

 * use is_nul() from coreutils rather then memcmp()

 * always call skip_hole() (SEEK_DATA)

 * fix possible overflows

Signed-off-by: Karel Zak <kzak@redhat.com>

diff --git a/sys-utils/fallocate.c b/sys-utils/fallocate.c
index a2545039ed14d1e8d6ddeea098c54464e7ea466b..e6dac1993e7e46a3b37b3138286dd35db86917dd 100644 (file)
--- a/sys-utils/fallocate.c
+++ b/sys-utils/fallocate.c
@@ -130,6 +130,27 @@ static int skip_hole(int fd, off_t *off)
        return -1;              /* no hole */
 }
 
+static int is_nul(void const *buf, size_t bufsize)
+{
+       typedef uintptr_t word;
+       void const *vp;
+       char const *cbuf = buf, *cp;
+       word const *wp = buf;
+
+       /* Find first nonzero *word*, or the word with the sentinel.  */
+       while (*wp++ == 0)
+               continue;
+
+       /* Find the first nonzero *byte*, or the sentinel.  */
+       vp = wp - 1;
+       cp = vp;
+
+       while (*cp++ == 0)
+               continue;
+
+         return cbuf + bufsize < cp;
+}
+
 static void dig_holes(int fd, off_t off, off_t len)
 {
        off_t end = len ? off + len : 0;
@@ -137,9 +158,8 @@ static void dig_holes(int fd, off_t off, off_t len)
        off_t cache_start = 0;
        uintmax_t ct = 0;
        size_t bufsz, cachesz;
-       char *buf, *empty;
+       char *buf;
        struct stat st;
-       int sparse = 0;
 
        if (fstat(fd, &st) != 0)
                err(EXIT_FAILURE, _("stat failed %s"), filename);
@@ -156,16 +176,10 @@ static void dig_holes(int fd, off_t off, off_t len)
         */
        cachesz = getpagesize() * 256;
 
-       if (st.st_blocks * 512 < st.st_size) {
-               if (verbose)
-                       fprintf(stdout, _("%s: already has holes.\n"), filename);
-               sparse = 1;
-       }
        if (lseek(fd, off, SEEK_SET) < 0)
                err(EXIT_FAILURE, _("seek on %s failed"), filename);
 
        buf = xmalloc(bufsz);
-       empty = xcalloc(1, bufsz);
        cache_start = off;
 
 #if defined(POSIX_FADV_SEQUENTIAL) && defined(HAVE_POSIX_FADVISE)
@@ -178,20 +192,18 @@ static void dig_holes(int fd, off_t off, off_t len)
                rsz = pread(fd, buf, bufsz, off);
                if (rsz < 0 && errno)
                        err(EXIT_FAILURE, _("%s: read failed"), filename);
-               if (end && rsz > 0 && off + rsz > end)
+               if (end && rsz > 0 && off > end - rsz)
                        rsz = end - off;
                if (rsz <= 0)
                        break;
 
-               if (memcmp(buf, empty, rsz) == 0) {
+               if (is_nul(buf, rsz)) {
                        if (!hole_sz) {                         /* new hole detected */
-                               if (sparse) {
-                                       int rc = skip_hole(fd, &off);
-                                       if (rc == 0)
-                                               continue;       /* hole skipped */
-                                       else if (rc == 1)
-                                               break;          /* end of file */
-                               }
+                               int rc = skip_hole(fd, &off);
+                               if (rc == 0)
+                                       continue;       /* hole skipped */
+                               else if (rc == 1)
+                                       break;          /* end of file */
                                hole_start = off;
                        }
                        hole_sz += rsz;
@@ -222,7 +234,6 @@ static void dig_holes(int fd, off_t off, off_t len)
        }
 
        free(buf);
-       free(empty);
 
        if (verbose) {
                char *str = size_to_human_string(SIZE_SUFFIX_3LETTER | SIZE_SUFFIX_SPACE, ct);