+static int read_cow_bitmap(int fd, void *buf, int offset, int len)
+{
+ int err;
+
+ err = os_seek_file(fd, offset);
+ if (err < 0)
+ return err;
+
+ err = os_read_file(fd, buf, len);
+ if (err < 0)
+ return err;
+
+ return 0;
+}
+
+static int backing_file_mismatch(char *file, __u64 size, time_t mtime)
+{
+ unsigned long modtime;
+ unsigned long long actual;
+ int err;
+
+ err = os_file_modtime(file, &modtime);
+ if (err < 0) {
+ printk(KERN_ERR "Failed to get modification time of backing "
+ "file \"%s\", err = %d\n", file, -err);
+ return err;
+ }
+
+ err = os_file_size(file, &actual);
+ if (err < 0) {
+ printk(KERN_ERR "Failed to get size of backing file \"%s\", "
+ "err = %d\n", file, -err);
+ return err;
+ }
+
+ if (actual != size) {
+ /*__u64 can be a long on AMD64 and with %lu GCC complains; so
+ * the typecast.*/
+ printk(KERN_ERR "Size mismatch (%llu vs %llu) of COW header "
+ "vs backing file\n", (unsigned long long) size, actual);
+ return -EINVAL;
+ }
+ if (modtime != mtime) {
+ printk(KERN_ERR "mtime mismatch (%ld vs %ld) of COW header vs "
+ "backing file\n", mtime, modtime);
+ return -EINVAL;
+ }
+ return 0;
+}
+
+static int path_requires_switch(char *from_cmdline, char *from_cow, char *cow)
+{
+ struct uml_stat buf1, buf2;
+ int err;
+
+ if (from_cmdline == NULL)
+ return 0;
+ if (!strcmp(from_cmdline, from_cow))
+ return 0;
+
+ err = os_stat_file(from_cmdline, &buf1);
+ if (err < 0) {
+ printk(KERN_ERR "Couldn't stat '%s', err = %d\n", from_cmdline,
+ -err);
+ return 0;
+ }
+ err = os_stat_file(from_cow, &buf2);
+ if (err < 0) {
+ printk(KERN_ERR "Couldn't stat '%s', err = %d\n", from_cow,
+ -err);
+ return 1;
+ }
+ if ((buf1.ust_dev == buf2.ust_dev) && (buf1.ust_ino == buf2.ust_ino))
+ return 0;
+
+ printk(KERN_ERR "Backing file mismatch - \"%s\" requested, "
+ "\"%s\" specified in COW header of \"%s\"\n",
+ from_cmdline, from_cow, cow);
+ return 1;
+}
+
+static int open_ubd_file(char *file, struct openflags *openflags, int shared,
+ char **backing_file_out, int *bitmap_offset_out,
+ unsigned long *bitmap_len_out, int *data_offset_out,
+ int *create_cow_out)
+{
+ time_t mtime;
+ unsigned long long size;
+ __u32 version, align;
+ char *backing_file;
+ int fd, err, sectorsize, asked_switch, mode = 0644;
+
+ fd = os_open_file(file, *openflags, mode);
+ if (fd < 0) {
+ if ((fd == -ENOENT) && (create_cow_out != NULL))
+ *create_cow_out = 1;
+ if (!openflags->w ||
+ ((fd != -EROFS) && (fd != -EACCES)))
+ return fd;
+ openflags->w = 0;
+ fd = os_open_file(file, *openflags, mode);
+ if (fd < 0)
+ return fd;
+ }
+
+ if (shared)
+ printk(KERN_INFO "Not locking \"%s\" on the host\n", file);
+ else {
+ err = os_lock_file(fd, openflags->w);
+ if (err < 0) {
+ printk(KERN_ERR "Failed to lock '%s', err = %d\n",
+ file, -err);
+ goto out_close;
+ }
+ }
+
+ /* Successful return case! */
+ if (backing_file_out == NULL)
+ return fd;
+
+ err = read_cow_header(file_reader, &fd, &version, &backing_file, &mtime,
+ &size, §orsize, &align, bitmap_offset_out);
+ if (err && (*backing_file_out != NULL)) {
+ printk(KERN_ERR "Failed to read COW header from COW file "
+ "\"%s\", errno = %d\n", file, -err);
+ goto out_close;
+ }
+ if (err)
+ return fd;
+
+ asked_switch = path_requires_switch(*backing_file_out, backing_file,
+ file);
+
+ /* Allow switching only if no mismatch. */
+ if (asked_switch && !backing_file_mismatch(*backing_file_out, size,
+ mtime)) {
+ printk(KERN_ERR "Switching backing file to '%s'\n",
+ *backing_file_out);
+ err = write_cow_header(file, fd, *backing_file_out,
+ sectorsize, align, &size);
+ if (err) {
+ printk(KERN_ERR "Switch failed, errno = %d\n", -err);
+ goto out_close;
+ }
+ } else {
+ *backing_file_out = backing_file;
+ err = backing_file_mismatch(*backing_file_out, size, mtime);
+ if (err)
+ goto out_close;
+ }
+
+ cow_sizes(version, size, sectorsize, align, *bitmap_offset_out,
+ bitmap_len_out, data_offset_out);
+
+ return fd;
+ out_close:
+ os_close_file(fd);
+ return err;
+}
+
+static int create_cow_file(char *cow_file, char *backing_file,
+ struct openflags flags,
+ int sectorsize, int alignment, int *bitmap_offset_out,
+ unsigned long *bitmap_len_out, int *data_offset_out)
+{
+ int err, fd;
+
+ flags.c = 1;
+ fd = open_ubd_file(cow_file, &flags, 0, NULL, NULL, NULL, NULL, NULL);
+ if (fd < 0) {
+ err = fd;
+ printk(KERN_ERR "Open of COW file '%s' failed, errno = %d\n",
+ cow_file, -err);
+ goto out;
+ }
+
+ err = init_cow_file(fd, cow_file, backing_file, sectorsize, alignment,
+ bitmap_offset_out, bitmap_len_out,
+ data_offset_out);
+ if (!err)
+ return fd;
+ os_close_file(fd);
+ out:
+ return err;
+}
+