[PATCH] cifs-utils: smbinfo: add gettconinfo command

[Anthony Nandaa <profnandaa@gmail.com>]

As a follow up on the patch on Linux: de4eceab578e
("smb3: allow dumping session and tcon id to improve stats analysis
and debugging") [1]

Add `gettconinfo` command to dump both the TCON Id and Session Id of
a given SMB mount; to help with correlation in cases when multiple
mounts are to the same share.

Example run:
```
./smbinfo gettconinfo /mnt/smb_share
TCON Id: 0x1
Session Id: 0xa40000000001
```

[1] https://github.com/torvalds/linux/commit/de4eceab578ead12a71e5b5588a57e142bbe8ceb

Cc: Pavel Shilovsky <pshilovsky@samba.org>
Cc: Steve French <stfrench@microsoft.com>
Signed-off-by: Anthony Nandaa <profnandaa@gmail.com>
---
 smbinfo     | 29 +++++++++++++++++++++++++++++
 smbinfo.rst |  2 ++
 2 files changed, 31 insertions(+)

diff --git a/smbinfo b/smbinfo
index 73c5bb3..3467b0b 100755
--- a/smbinfo
+++ b/smbinfo
@@ -35,6 +35,7 @@ CIFS_QUERY_INFO          = 0xc018cf07
 CIFS_ENUMERATE_SNAPSHOTS = 0x800ccf06
 CIFS_DUMP_KEY            = 0xc03acf08
 CIFS_DUMP_FULL_KEY       = 0xc011cf0a
+CIFS_GET_TCON_INFO       = 0x800ccf0c
 
 # large enough input buffer length
 INPUT_BUFFER_LENGTH = 16384
@@ -289,6 +290,10 @@ def main():
     sap.add_argument("file")
     sap.set_defaults(func=cmd_keys)
 
+    sap = subp.add_parser("gettconinfo", help="Prints TCON Id and Session Id for a cifs file")
+    sap.add_argument("file")
+    sap.set_defaults(func=cmd_gettconinfo)
+
     # parse arguments
     args = ap.parse_args()
 
@@ -876,5 +881,29 @@ def cmd_keys(args):
         print("ServerIn  Key: %s"%bytes_to_hex(kd.server_in_key))
         print("ServerOut key: %s"%bytes_to_hex(kd.server_out_key))
 
+class SmbMntTconInfoStruct:
+    def __init__(self):
+        self.tid = 0
+        self.session_id = 0
+
+    def ioctl(self, fd):
+        buf = bytearray()
+        buf.extend(struct.pack("=IQ", self.tid, self.session_id))
+        fcntl.ioctl(fd, CIFS_GET_TCON_INFO, buf, True)
+        (self.tid, self.session_id) = struct.unpack_from('=IQ', buf, 0)
+
+def cmd_gettconinfo(args):
+    fd = os.open(args.file, os.O_RDONLY)
+    tcon = SmbMntTconInfoStruct()
+
+    try:
+        tcon.ioctl(fd)
+    except Exception as e:
+        print("syscall failed: %s"%e)
+        return False
+
+    print("TCON Id: 0x%x"%tcon.tid)
+    print("Session Id: 0x%x"%tcon.session_id)
+
 if __name__ == '__main__':
     main()
diff --git a/smbinfo.rst b/smbinfo.rst
index 1acf3c4..17270c5 100644
--- a/smbinfo.rst
+++ b/smbinfo.rst
@@ -96,6 +96,8 @@ COMMAND
 the SMB3 traffic of this mount can be decryped e.g. via wireshark
 (requires root).
 
+`gettconinfo`: Prints both the TCON Id and Session Id for a cifs file.
+
 *****
 NOTES
 *****
-- 
2.34.1