smb3: allow previous versions to be mounted with snapshot= mount parm

mounting with the "snapshots=" mount parm allows a read-only
view of a previous version of a file system (see MS-SMB2
and "timewarp" tokens, section 2.2.13.2.6) based on the timestamp
passed in on the snapshots mount parm.

Add processing to optionally send this create context.

Example output:

/mnt1 is mounted with "snapshots=..." and will see an earlier
version of the directory, with three fewer files than /mnt2
the current version of the directory.

root@Ubuntu-17-Virtual-Machine:~/cifs-2.6# cat /proc/mounts | grep cifs
//172.22.149.186/public /mnt1 cifs
ro,relatime,vers=default,cache=strict,username=smfrench,uid=0,noforceuid,gid=0,noforcegid,addr=172.22.149.186,file_mode=0755,dir_mode=0755,soft,nounix,mapposix,rsize=1048576,wsize=1048576,echo_interval=60,snapshot=131748608570000000,actimeo=1

//172.22.149.186/public /mnt2 cifs
rw,relatime,vers=default,cache=strict,username=smfrench,uid=0,noforceuid,gid=0,noforcegid,addr=172.22.149.186,file_mode=0755,dir_mode=0755,soft,nounix,mapposix,rsize=1048576,wsize=1048576,echo_interval=60,actimeo=1

root@Ubuntu-17-Virtual-Machine:~/cifs-2.6# ls /mnt1
EmptyDir  newerdir
root@Ubuntu-17-Virtual-Machine:~/cifs-2.6# ls /mnt1/newerdir

root@Ubuntu-17-Virtual-Machine:~/cifs-2.6# ls /mnt2
EmptyDir  file  newerdir  newestdir  timestamp-trace.cap
root@Ubuntu-17-Virtual-Machine:~/cifs-2.6# ls /mnt2/newerdir
new-file-not-in-snapshot

Snapshots are extremely useful for comparing previous versions of files or directories,
and recovering from data corruptions or mistakes.

Signed-off-by: Steve French <stfrench@microsoft.com>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>

diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index faf2b77..2f19380 100644 (file)
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -1856,6 +1856,51 @@ add_durable_context(struct kvec *iov, unsigned int *num_iovec,
        return 0;
 }
 
+/* See MS-SMB2 2.2.13.2.7 */
+static struct crt_twarp_ctxt *
+create_twarp_buf(__u64 timewarp)
+{
+       struct crt_twarp_ctxt *buf;
+
+       buf = kzalloc(sizeof(struct crt_twarp_ctxt), GFP_KERNEL);
+       if (!buf)
+               return NULL;
+
+       buf->ccontext.DataOffset = cpu_to_le16(offsetof
+                                       (struct crt_twarp_ctxt, Timestamp));
+       buf->ccontext.DataLength = cpu_to_le32(8);
+       buf->ccontext.NameOffset = cpu_to_le16(offsetof
+                               (struct crt_twarp_ctxt, Name));
+       buf->ccontext.NameLength = cpu_to_le16(4);
+       /* SMB2_CREATE_TIMEWARP_TOKEN is "TWrp" */
+       buf->Name[0] = 'T';
+       buf->Name[1] = 'W';
+       buf->Name[2] = 'r';
+       buf->Name[3] = 'p';
+       buf->Timestamp = cpu_to_le64(timewarp);
+       return buf;
+}
+
+/* See MS-SMB2 2.2.13.2.7 */
+static int
+add_twarp_context(struct kvec *iov, unsigned int *num_iovec, __u64 timewarp)
+{
+       struct smb2_create_req *req = iov[0].iov_base;
+       unsigned int num = *num_iovec;
+
+       iov[num].iov_base = create_twarp_buf(timewarp);
+       if (iov[num].iov_base == NULL)
+               return -ENOMEM;
+       iov[num].iov_len = sizeof(struct crt_twarp_ctxt);
+       if (!req->CreateContextsOffset)
+               req->CreateContextsOffset = cpu_to_le32(
+                               sizeof(struct smb2_create_req) +
+                               iov[num - 1].iov_len);
+       le32_add_cpu(&req->CreateContextsLength, sizeof(struct crt_twarp_ctxt));
+       *num_iovec = num + 1;
+       return 0;
+}
+
 static int
 alloc_path_with_tree_prefix(__le16 **out_path, int *out_size, int *out_len,
                            const char *treename, const __le16 *path)
@@ -2168,6 +2213,21 @@ SMB2_open_init(struct cifs_tcon *tcon, struct smb_rqst *rqst, __u8 *oplock,
                        return rc;
        }
 
+       if (tcon->snapshot_time) {
+               cifs_dbg(FYI, "adding snapshot context\n");
+               if (n_iov > 2) {
+                       struct create_context *ccontext =
+                           (struct create_context *)iov[n_iov-1].iov_base;
+                       ccontext->Next =
+                               cpu_to_le32(iov[n_iov-1].iov_len);
+               }
+
+               rc = add_twarp_context(iov, &n_iov, tcon->snapshot_time);
+               if (rc)
+                       return rc;
+       }
+
+
        rqst->rq_nvec = n_iov;
        return 0;
 }

diff --git a/fs/cifs/smb2pdu.h b/fs/cifs/smb2pdu.h
index cf37c2f..a2eeae9 100644 (file)
--- a/fs/cifs/smb2pdu.h
+++ b/fs/cifs/smb2pdu.h
@@ -767,6 +767,14 @@ struct create_durable_handle_reconnect_v2 {
        struct durable_reconnect_context_v2 dcontext;
 } __packed;
 
+/* See MS-SMB2 2.2.13.2.5 */
+struct crt_twarp_ctxt {
+       struct create_context ccontext;
+       __u8    Name[8];
+       __le64  Timestamp;
+
+} __packed;
+
 #define COPY_CHUNK_RES_KEY_SIZE        24
 struct resume_key_req {
        char ResumeKey[COPY_CHUNK_RES_KEY_SIZE];