ceph: new mount option to disable usage of copy-from op

Add a new mount option 'nocopyfrom' that will prevent the usage of the
RADOS 'copy-from' operation in cephfs. This could be useful, for example,
for an administrator to temporarily mitigate any possible bugs in the
'copy-from' implementation.

Currently, only copy_file_range uses this RADOS operation. Setting this
mount option will result in this syscall reverting to the default VFS
implementation, i.e. to perform the copies locally instead of doing remote
object copies.

Signed-off-by: Luis Henriques <[e-mail]>
Reviewed-by: "Yan, Zheng" <[e-mail]>
Signed-off-by: Ilya Dryomov <[e-mail]>

Documentation/filesystems/ceph.txt

···
         Report overall filesystem usage in statfs instead of using the root
         directory quota.
 
+  nocopyfrom
+        Don't use the RADOS 'copy-from' operation to perform remote object
+        copies.  Currently, it's only used in copy_file_range, which will revert
+        to the default VFS implementation if this option is used.
+
 More Information
 ================
 

fs/ceph/file.c

···
 	 * efficient).
 	 */
 
+	if (ceph_test_mount_opt(ceph_inode_to_client(src_inode), NOCOPYFROM))
+		return -EOPNOTSUPP;
+
 	if ((src_ci->i_layout.stripe_unit != dst_ci->i_layout.stripe_unit) ||
 	    (src_ci->i_layout.stripe_count != dst_ci->i_layout.stripe_count) ||
 	    (src_ci->i_layout.object_size != dst_ci->i_layout.object_size))

fs/ceph/super.c

···
 	Opt_noacl,
 	Opt_quotadf,
 	Opt_noquotadf,
+	Opt_copyfrom,
+	Opt_nocopyfrom,
 };
 
 static match_table_t fsopt_tokens = {
···
 	{Opt_noacl, "noacl"},
 	{Opt_quotadf, "quotadf"},
 	{Opt_noquotadf, "noquotadf"},
+	{Opt_copyfrom, "copyfrom"},
+	{Opt_nocopyfrom, "nocopyfrom"},
 	{-1, NULL}
 };
 
···
 		break;
 	case Opt_noquotadf:
 		fsopt->flags |= CEPH_MOUNT_OPT_NOQUOTADF;
+		break;
+	case Opt_copyfrom:
+		fsopt->flags &= ~CEPH_MOUNT_OPT_NOCOPYFROM;
+		break;
+	case Opt_nocopyfrom:
+		fsopt->flags |= CEPH_MOUNT_OPT_NOCOPYFROM;
 		break;
 #ifdef CONFIG_CEPH_FS_POSIX_ACL
 	case Opt_acl:
···
 	else
 		seq_puts(m, ",noacl");
 #endif
+
+	if (fsopt->flags & CEPH_MOUNT_OPT_NOCOPYFROM)
+		seq_puts(m, ",nocopyfrom");
 
 	if (fsopt->mds_namespace)
 		seq_show_option(m, "mds_namespace", fsopt->mds_namespace);

fs/ceph/super.h

···
 #define CEPH_MOUNT_OPT_NOPOOLPERM      (1<<11) /* no pool permission check */
 #define CEPH_MOUNT_OPT_MOUNTWAIT       (1<<12) /* mount waits if no mds is up */
 #define CEPH_MOUNT_OPT_NOQUOTADF       (1<<13) /* no root dir quota in statfs */
+#define CEPH_MOUNT_OPT_NOCOPYFROM      (1<<14) /* don't use RADOS 'copy-from' op */
 
 #define CEPH_MOUNT_OPT_DEFAULT    CEPH_MOUNT_OPT_DCACHE