verify: add faster 'memory is all zeroes' helper

Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/verify.c b/verify.c
index ee9160c673c3fa4efab1a48dea8eedbe7f939473..19bec75a4ec75d29e2af196f4ad41791a97efceb 100644 (file)
--- a/verify.c
+++ b/verify.c
@@ -661,38 +661,63 @@ int verify_io_u_async(struct thread_data *td, struct io_u **io_u_ptr)
        return 0;
 }
 
+/*
+ * Thanks Rusty, for spending the time so I don't have to.
+ *
+ * http://rusty.ozlabs.org/?p=560
+ */
+static int mem_is_zero(const void *data, size_t length)
+{
+       const unsigned char *p = data;
+       size_t len;
+
+       /* Check first 16 bytes manually */
+       for (len = 0; len < 16; len++) {
+               if (!length)
+                       return 1;
+               if (*p)
+                       return 0;
+               p++;
+               length--;
+       }
+
+       /* Now we know that's zero, memcmp with self. */
+       return memcmp(data, p, length) == 0;
+}
+
+static int mem_is_zero_slow(const void *data, size_t length, size_t *offset)
+{
+       const unsigned char *p = data;
+
+       *offset = 0;
+       while (length) {
+               if (*p)
+                       break;
+               (*offset)++;
+               length--;
+               p++;
+       }
+
+       return !length;
+}
+
 static int verify_trimmed_io_u(struct thread_data *td, struct io_u *io_u)
 {
-       static char zero_buf[1024];
-       unsigned int this_len, len;
-       int ret = 0;
-       void *p;
+       size_t offset;
 
        if (!td->o.trim_zero)
                return 0;
 
-       len = io_u->buflen;
-       p = io_u->buf;
-       do {
-               this_len = sizeof(zero_buf);
-               if (this_len > len)
-                       this_len = len;
-               if (memcmp(p, zero_buf, this_len)) {
-                       ret = EILSEQ;
-                       break;
-               }
-               len -= this_len;
-               p += this_len;
-       } while (len);
-
-       if (!ret)
+       if (mem_is_zero(io_u->buf, io_u->buflen))
                return 0;
 
+       mem_is_zero_slow(io_u->buf, io_u->buflen, &offset);
+
        log_err("trim: verify failed at file %s offset %llu, length %lu"
                ", block offset %lu\n",
                        io_u->file->file_name, io_u->offset, io_u->buflen,
-                       (unsigned long) (p - io_u->buf));
-       return ret;
+                       (unsigned long) offset);
+       return EILSEQ;
 }
 
 static int verify_header(struct io_u *io_u, struct thread_data *td,