typedef int (*volume_identify_t)(struct volume *v);
typedef int (*volume_read_t)(struct volume *v, void *buf, int offset, int length);
typedef int (*volume_write_t)(struct volume *v, void *buf, int offset, int length);
typedef int (*volume_identify_t)(struct volume *v);
typedef int (*volume_read_t)(struct volume *v, void *buf, int offset, int length);
typedef int (*volume_write_t)(struct volume *v, void *buf, int offset, int length);