block/file-posix: Extract raw_regular_truncate()

This functionality is part of raw_create() which we will be able to
reuse nicely in raw_truncate().

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20170613202107.10125-7-mreitz@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>

block/file-posix.c

@@ -1624,6 +1624,81 @@ static void raw_close(BlockDriverState *bs)
     }
 }
 
+static int raw_regular_truncate(int fd, int64_t offset, PreallocMode prealloc,
+                                Error **errp)
+{
+    int result = 0;
+    char *buf;
+
+    switch (prealloc) {
+#ifdef CONFIG_POSIX_FALLOCATE
+    case PREALLOC_MODE_FALLOC:
+        /*
+         * Truncating before posix_fallocate() makes it about twice slower on
+         * file systems that do not support fallocate(), trying to check if a
+         * block is allocated before allocating it, so don't do that here.
+         */
+        result = -posix_fallocate(fd, 0, offset);
+        if (result != 0) {
+            /* posix_fallocate() doesn't set errno. */
+            error_setg_errno(errp, -result,
+                             "Could not preallocate data for the new file");
+        }
+        return result;
+#endif
+    case PREALLOC_MODE_FULL:
+    {
+        int64_t num = 0, left = offset;
+
+        /*
+         * Knowing the final size from the beginning could allow the file
+         * system driver to do less allocations and possibly avoid
+         * fragmentation of the file.
+         */
+        if (ftruncate(fd, offset) != 0) {
+            result = -errno;
+            error_setg_errno(errp, -result, "Could not resize file");
+            return result;
+        }
+
+        buf = g_malloc0(65536);
+
+        while (left > 0) {
+            num = MIN(left, 65536);
+            result = write(fd, buf, num);
+            if (result < 0) {
+                result = -errno;
+                error_setg_errno(errp, -result,
+                                 "Could not write to the new file");
+                break;
+            }
+            left -= result;
+        }
+        if (result >= 0) {
+            result = fsync(fd);
+            if (result < 0) {
+                result = -errno;
+                error_setg_errno(errp, -result,
+                                 "Could not flush new file to disk");
+            }
+        }
+        g_free(buf);
+        return result;
+    }
+    case PREALLOC_MODE_OFF:
+        if (ftruncate(fd, offset) != 0) {
+            result = -errno;
+            error_setg_errno(errp, -result, "Could not resize file");
+        }
+        return result;
+    default:
+        result = -ENOTSUP;
+        error_setg(errp, "Unsupported preallocation mode: %s",
+                   PreallocMode_lookup[prealloc]);
+        return result;
+    }
+}
+
 static int raw_truncate(BlockDriverState *bs, int64_t offset,
                         PreallocMode prealloc, Error **errp)
 {
@@ -1892,72 +1967,9 @@ static int raw_create(const char *filename, QemuOpts *opts, Error **errp)
 #endif
     }
 
-    switch (prealloc) {
-#ifdef CONFIG_POSIX_FALLOCATE
-    case PREALLOC_MODE_FALLOC:
-        /*
-         * Truncating before posix_fallocate() makes it about twice slower on
-         * file systems that do not support fallocate(), trying to check if a
-         * block is allocated before allocating it, so don't do that here.
-         */
-        result = -posix_fallocate(fd, 0, total_size);
-        if (result != 0) {
-            /* posix_fallocate() doesn't set errno. */
-            error_setg_errno(errp, -result,
-                             "Could not preallocate data for the new file");
-        }
-        break;
-#endif
-    case PREALLOC_MODE_FULL:
-    {
-        int64_t num = 0, left = total_size;
-
-        /*
-         * Knowing the final size from the beginning could allow the file
-         * system driver to do less allocations and possibly avoid
-         * fragmentation of the file.
-         */
-        if (ftruncate(fd, total_size) != 0) {
-            result = -errno;
-            error_setg_errno(errp, -result, "Could not resize file");
-            goto out_close;
-        }
-
-        buf = g_malloc0(65536);
-
-        while (left > 0) {
-            num = MIN(left, 65536);
-            result = write(fd, buf, num);
-            if (result < 0) {
-                result = -errno;
-                error_setg_errno(errp, -result,
-                                 "Could not write to the new file");
-                break;
-            }
-            left -= result;
-        }
-        if (result >= 0) {
-            result = fsync(fd);
-            if (result < 0) {
-                result = -errno;
-                error_setg_errno(errp, -result,
-                                 "Could not flush new file to disk");
-            }
-        }
-        g_free(buf);
-        break;
-    }
-    case PREALLOC_MODE_OFF:
-        if (ftruncate(fd, total_size) != 0) {
-            result = -errno;
-            error_setg_errno(errp, -result, "Could not resize file");
-        }
-        break;
-    default:
-        result = -ENOTSUP;
-        error_setg(errp, "Unsupported preallocation mode: %s",
-                   PreallocMode_lookup[prealloc]);
-        break;
+    result = raw_regular_truncate(fd, total_size, prealloc, errp);
+    if (result < 0) {
+        goto out_close;
     }
 
 out_close: