struct_obd_connect_data.txt

OBD Connect Data
^^^^^^^^^^^^^^^^
An 'obd_connect_data' structure accompanies every connect operation in
both the request message and in the reply message.  It contains the
mutually supported features that are negotiated between the client and
server at *_CONNECT time.

.The OBD Connect Data Structure
[[struct-obd-connect-data]]
****
[source,c]
----
struct obd_connect_data {
    __u64 ocd_connect_flags;
    __u32 ocd_version;      /* OBD_CONNECT_VERSION */
    __u32 ocd_grant;        /* OBD_CONNECT_GRANT */
    __u32 ocd_index;        /* OBD_CONNECT_INDEX */
    __u32 ocd_brw_size;     /* OBD_CONNECT_BRW_SIZE */
    __u64 ocd_ibits_known;  /* OBD_CONNECT_IBITS */
    __u8  ocd_blocksize;    /* OBD_CONNECT_GRANT_PARAM */
    __u8  ocd_inodespace;   /* OBD_CONNECT_GRANT_PARAM */
    __u16 ocd_grant_extent; /* OBD_CONNECT_GRANT_PARAM */
    __u32 ocd_unused;
    __u64 ocd_transno;      /* OBD_CONNECT_TRANSNO */
    __u32 ocd_group;        /* OBD_CONNECT_MDS */
    __u32 ocd_cksum_types;  /* OBD_CONNECT_CKSUM */
    __u32 ocd_max_easize;   /* OBD_CONNECT_MAX_EASIZE */
    __u32 ocd_instance;
    __u64 ocd_maxbytes;     /* OBD_CONNECT_MAXBYTES */
    __u64 padding1;
    __u64 padding2;
    __u64 padding3;
    __u64 padding4;
    __u64 padding5;
    __u64 padding6;
    __u64 padding7;
    __u64 padding8;
    __u64 padding9;
    __u64 paddingA;
    __u64 paddingB;
    __u64 paddingC;
    __u64 paddingD;
    __u64 paddingE;
    __u64 paddingF;
};
----
****

At *_CONNECT time the client sends in its request 'ocd_connect_flags'
the flags for all features that it understands and intends to use (for
example 'OBD_CONNECT_RDONLY' is optional depending on client mount
options).  The request also contains other fields that are only valid
if the matching flag is set.  The server replies in 'ocd_connect_flags'
with the subset of feature flags that it understands and intends to honor.
The server may set fields in the reply for mutually-understood features.

The 'ocd_connect_flags' field encodes the connect flags giving the
capabilities of a connection between client and target. Several of
those flags (noted in comments above and the discussion below)
actually control whether the remaining fields of 'obd_connect_data'
get used.  The [[obd-connect-flags]] flags are:

[source,c]
----
#define OBD_CONNECT_RDONLY                0x1ULL /*client has read-only access*/
#define OBD_CONNECT_INDEX                 0x2ULL /*connect specific LOV idx */
#define OBD_CONNECT_MDS                   0x4ULL /*connect from MDT to OST */
#define OBD_CONNECT_GRANT                 0x8ULL /*OSC gets grant at connect */
#define OBD_CONNECT_SRVLOCK              0x10ULL /*server takes locks for cli */
#define OBD_CONNECT_VERSION              0x20ULL /*Lustre versions in ocd */
#define OBD_CONNECT_REQPORTAL            0x40ULL /*Separate non-IO req portal */
#define OBD_CONNECT_ACL                  0x80ULL /*access control lists */
#define OBD_CONNECT_XATTR               0x100ULL /*client use extended attr */
#define OBD_CONNECT_TRUNCLOCK           0x400ULL /*locks on server for punch */
#define OBD_CONNECT_TRANSNO             0x800ULL /*replay sends init transno */
#define OBD_CONNECT_IBITS              0x1000ULL /*support for inodebits locks*/
#define OBD_CONNECT_ATTRFID            0x4000ULL /*Server can GetAttr By Fid*/
#define OBD_CONNECT_NODEVOH            0x8000ULL /*No open hndl on specl nodes*/
#define OBD_CONNECT_RMT_CLIENT        0x10000ULL /*Remote client */
#define OBD_CONNECT_RMT_CLIENT_FORCE  0x20000ULL /*Remote client by force */
#define OBD_CONNECT_BRW_SIZE          0x40000ULL /*Max bytes per rpc */
#define OBD_CONNECT_QUOTA64           0x80000ULL /*Not used since 2.4 */
#define OBD_CONNECT_CANCELSET        0x400000ULL /*Early batched cancels. */
#define OBD_CONNECT_SOM              0x800000ULL /*Size on MDS */
#define OBD_CONNECT_AT              0x1000000ULL /*client uses AT */
#define OBD_CONNECT_LRU_RESIZE      0x2000000ULL /*LRU resize feature. */
#define OBD_CONNECT_MDS_MDS         0x4000000ULL /*MDS-MDS connection */
#define OBD_CONNECT_REAL            0x8000000ULL /*real connection */
#define OBD_CONNECT_CHANGE_QS      0x10000000ULL /*Not used since 2.4 */
#define OBD_CONNECT_CKSUM          0x20000000ULL /*support several cksum algos*/
#define OBD_CONNECT_FID            0x40000000ULL /*FID is supported by server */
#define OBD_CONNECT_VBR            0x80000000ULL /*version based recovery */
#define OBD_CONNECT_LOV_V3        0x100000000ULL /*client supports LOV v3 EA */
#define OBD_CONNECT_GRANT_SHRINK  0x200000000ULL /* support grant shrink */
#define OBD_CONNECT_SKIP_ORPHAN   0x400000000ULL /* don't reuse orphan objids */
#define OBD_CONNECT_MAX_EASIZE    0x800000000ULL /* preserved for large EA */
#define OBD_CONNECT_FULL20       0x1000000000ULL /* it is 2.0 client */
#define OBD_CONNECT_LAYOUTLOCK   0x2000000000ULL /* client uses layout lock */
#define OBD_CONNECT_64BITHASH    0x4000000000ULL /* client supports 64-bits
                                                  * directory hash */
#define OBD_CONNECT_MAXBYTES     0x8000000000ULL /* max stripe size */
#define OBD_CONNECT_IMP_RECOV   0x10000000000ULL /* imp recovery support */
#define OBD_CONNECT_JOBSTATS    0x20000000000ULL /* jobid in ptlrpc_body */
#define OBD_CONNECT_UMASK       0x40000000000ULL /* create uses client umask */
#define OBD_CONNECT_EINPROGRESS 0x80000000000ULL /* client handles -EINPROGRESS
                                                  * RPC error properly */
#define OBD_CONNECT_GRANT_PARAM 0x100000000000ULL/* extra grant params used for
                                                  * finer space reservation */
#define OBD_CONNECT_FLOCK_OWNER 0x200000000000ULL /* for the fixed 1.8
                           * policy and 2.x server */
#define OBD_CONNECT_LVB_TYPE    0x400000000000ULL /* variable type of LVB */
#define OBD_CONNECT_NANOSEC_TIME 0x800000000000ULL /* nanosecond timestamps */
#define OBD_CONNECT_LIGHTWEIGHT 0x1000000000000ULL/* lightweight connection */
#define OBD_CONNECT_SHORTIO     0x2000000000000ULL/* short io */
#define OBD_CONNECT_PINGLESS    0x4000000000000ULL/* pings not required */
#define OBD_CONNECT_FLOCK_DEAD    0x8000000000000ULL/* deadlock detection */
#define OBD_CONNECT_DISP_STRIPE 0x10000000000000ULL/* create stripe disposition*/
#define OBD_CONNECT_OPEN_BY_FID    0x20000000000000ULL /* open by fid won't pack
                               name in request */
----

Each flag corresponds to a particular capability that the client and
target together will honor. A client will send a message including
some subset of these capabilities during a connection request to a
specific target. This tells the server what capabilities it has. The
server then replies with the subset of those capabilities it agrees to
honor (for the given target).

If the 'OBD_CONNECT_VERSION' flag is set then the 'ocd_version' field
is valid. The 'ocd_version' gives an encoding of the Lustre
version. The Lustre version itself is a four-tuple of decimal numbers
(major, minor, patch, fix), with missing trailing values defaulting to
zero. Each of the four numbers is shifted into place in the four bytes
of the 'ocd_version'.  For example, Version 2.7.55 would be
hexadecimal number 0x02073700.

If the OBD_CONNECT_GRANT flag is set then the 'ocd_grant' field is
valid. The 'ocd_grant' value in a reply (to a connection request)
initializes the client's grant. See <<grant>>.

If the OBD_CONNECT_INDEX flag is set then the 'ocd_index' field is
valid. The 'ocd_index' value is set in a request to hold the LOV
index of the OST or the LMV index of the MDT.  The server's export for
the target holds the correct value, and if the client sends a value
that does not match the server returns the -EBADF error.

If the OBD_CONNECT_BRW_SIZE flag is set then the 'ocd_brw_size' field
is valid. The 'ocd_brw_size' value sets the maximum supported bulk
transfer size. The client proposes a value in its connection request,
and the server's reply will either accept the requested size or
further limit the size.  The server will not increase the client's
requested maximum bulk transfer size.

If the OBD_CONNECT_IBITS flag is set then the 'ocd_ibits_known' field
is valid. The 'ocd_ibits_known' flags determine the handling of
locks on MDS inodes.  The OBD_CONNECT_IBITS flag was introduced in
Lustre 1.4 and is mandatory for MDS_CONNECT RPCs.

[source,c]
----
#define MDS_INODELOCK_LOOKUP 0x000001	/* For namespace, dentry etc, and also
					 * was used to protect permission (mode,
					 * owner, group etc) before 2.4. */
#define MDS_INODELOCK_UPDATE 0x000002	/* size, links, timestamps */
#define MDS_INODELOCK_OPEN   0x000004	/* For opened files */
#define MDS_INODELOCK_LAYOUT 0x000008	/* for layout */
#define MDS_INODELOCK_PERM   0x000010	/* separate permission bits */
#define MDS_INODELOCK_XATTR  0x000020	/* extended attributes */
----

//////////////////////////////////////////////////////////////////////
/* The PERM bit is added int 2.4, and it is used to protect permission(mode,
 * owner, group, acl etc), so to separate the permission from LOOKUP lock.
 * Because for remote directories(in DNE), these locks will be granted by
 * different MDTs(different ldlm namespace).
 *
 * For local directory, MDT will always grant UPDATE_LOCK|PERM_LOCK together.
 * For Remote directory, the master MDT, where the remote directory is, will
 * grant UPDATE_LOCK|PERM_LOCK, and the remote MDT, where the name entry is,
 * will grant LOOKUP_LOCK. */
#define MDS_INODELOCK_PERM   0x000010
#define MDS_INODELOCK_XATTR  0x000020	/* extended attributes */
//////////////////////////////////////////////////////////////////////

If the OBD_CONNECT_GRANT_PARAM flag is set then the 'ocd_blocksize',
'ocd_inodespace', and 'ocd_grant_extent' fields are honored. A server
reply uses the 'ocd_blocksize' value to inform the client of the log
base two of the size in bytes of the OSD's blocks.

A server reply uses the 'ocd_inodespace' value to inform the client of
the log base two of the size of an inode.

Under some circumstances (for example when the OSD is ZFS) there may
be additional overhead in handling writes for each extent. The server
uses the 'ocd_grant_extent' value to inform the client of the size in
bytes consumed from its grant on the server when creating a new
file. The client uses this value in calculating how much dirty write
cache it has and whether it has reached the limit established by the
target's grant.

If the OBD_CONNECT_TRANSNO flag is set then the 'ocd_transno' field is
honored. A server uses the 'ocd_transno' value during recovery to
inform the client of the transaction number at which it should begin
replay.

If the OBD_CONNECT_MDS flag is set then the 'ocd_group' field is
valid. When an MDT connects to an OST the 'ocd_group' field informs
the OSS of the MDT's index. Objects on that OST for that MDT will be
in a common namespace served by that MDT.

If the OBD_CONNECT_CKSUM flag is set then the 'ocd_cksum_types' field
is valid. The client uses the 'ocd_cksum_types' field to propose
to the server the client's available (possibly hardware assisted)
checksum mechanisms. The server replies with the checksum types it has
available and that are most efficient on the server. The client may
employ any of the replied checksum algorithms for a given bulk transfer,
but will typically select the fastest of the agreed algorithms.

If the OBD_CONNECT_MAX_EASIZE flag is set then the 'ocd_max_easize'
field is valid. The server uses 'ocd_max_easize' to inform the
client about the amount of space that can be allocated in each inode
for extended attributes. The 'ocd_max_easize' specifically refers to
the space used for layout information. This allows the client to
determine the maximum layout size (and hence stripe count) that can be
stored on the MDT.

The 'ocd_instance' field (alone) is not governed by an OBD_CONNECT_*
flag. The MGS uses the 'ocd_instance' value in its reply to a
connection request to inform the server and target of the "era" of its
connection. The MGS initializes the era value for each server to zero
and increments that value every time the target connects. This
supports imperative recovery.

If the OBD_CONNECT_MAXBYTES flag is set then the 'ocd_maxbytes' field
is honored. An OSS uses the 'ocd_maxbytes' value to inform the client
of the maximum OST object size for this target.  A file that is striped
uniformly across multiple OST objects (RAID-0) cannot be larger than the
number of stripes times the minimum 'ocd_maxbytes' value from any of its
constituent objects.

The additional space in the 'obd_connect_data' structure is unused and
reserved for future use.

Other OBD_CONNECT_* flags have no corresponding field in
obd_connect_data but still control client-server supported features.

If the OBD_CONNECT_RDONLY flag is set then the client is mounted in
read-only mode and the server honors that by denying any modification
from this client.

If the OBD_CONNECT_SRVLOCK flag is set then the client and server
support lock-less IO. The server will take locks for client IO requests
with the OBD_BRW_SRVLOCK flag in the 'niobuf_remote' structure
flags. This is used for Direct IO or when there is significant lock
contention on a single OST object.  The client takes no LDLM lock and
delegates locking to the server.

If the OBD_CONNECT_ACL flag is set then the server supports the ACL
mount option for its file system. If the server is mounted with ACL
support but the client does not pass OBD_CONNECT_ACL then the client
mount is refused.

If the OBD_CONNECT_XATTR flag is set then the server supports user
extended attributes. This is requested by the client if mounted
with the appropriate mount option, but is enabled or disabled by the
mount options of the OSD for MDT0000.

If the OBD_CONNECT_TRUNCLOCK flag is set then the client and the
server support lock-less truncate. This is realized in an OST_PUNCH RPC
by setting the 'obdo' structure's 'o_flag' field to include the
OBD_FL_SRVLOCK. In that circumstance the client takes no lock, and the
server must take a lock on the resource while performing the truncate.

If the OBD_CONNECT_ATTRFID flag is set then the server supports
getattr requests by FID of file instead of name. This reduces
unnecessary RPCs for DNE and for file attribute revalidation after
a lock cancellation.

If the OBD_CONNECT_NODEVOH flag is set then the server provides no
open handle for block and character special inodes.

If the OBD_CONNECT_RMT_CLIENT is set then the client is set as
'remote' with respect to the server. The client is considered as
'local' if the user/group database on the client is identical to that
on the server, otherwise the client is set as 'remote'. This
terminology is part of Lustre Kerberos feature which is not supported
as of Lustre 2.7.

If the OBD_CONNECT_RMT_CLIENT_FORCE is set then client is set as
remote client forcefully. If the server security level doesn't support
remote clients then this client connect reply will return an -EACCESS
error.

If the OBD_CONNECT_CANCELSET is set then early batched cancels are
enabled.  The ELC (Early Lock Cancel) feature allows client locks to
be canceled prior the cancellation callback if it is clear that lock
is not needed anymore, for example after rename, after removing file
or directory, link, etc. This can reduce amount of RPCs significantly.

If the OBD_CONNECT_AT is set then client and server use 'Adaptive
Timeouts' during request processing. Servers keep track of the RPC
processing time and report this information back to clients to
estimate the time needed for future requests and set appropriate RPC
timeouts.

If the OBD_CONNECT_LRU_RESIZE is set then the LRU self-adjusting is
enabled.

If the OBD_CONNECT_FID is set then FID support is understood by the
client and server. This flag was introduced in Lustre 2.0 and
is required when connecting to any 2.0 or later server.  It is
understood by Lustre 1.8 clients.

If the OBD_CONNECT_VBR is set then version based recovery is used on
the server.  VBR stores the most recent transaction in which each
object was modified to track its changes on the server and to decide
if a replayed RPC can be applied during recovery or not. This helps
to complete recovery even if some clients were missed or evicted.
That flag is always set by clients since Lustre 1.8 and is used to
notify the server if client supports VBR.

If the OBD_CONNECT_LOV_V3 is set if the client supports LOV_MAGIC_V3
(0x0BD30BD0) style layouts. This type of the layout was introduced
along with OST pools support and added the 'lov_mds_md' layout. The
OBD_CONNECT_LOV_V3 flag notifies a server if client supports
this type of LOV EA to handle requests from it properly.

If the OBD_CONNECT_GRANT_SHRINK is set then the client can release
grant space when idle.

If the OBD_CONNECT_SKIP_ORPHAN is set then OST doesn't reuse orphan
object IDs after recovery. This connection flag is used between MDS
and OST to agree about an object pre-creation policy after MDS
recovery. If set, then if some of precreated objects weren't used
when an MDT was restarted then an OST must destroy any unused objects
rather than re-use those objects.

If the OBD_CONNECT_FULL20 is set then the client is Lustre 2.x client.
Clients that are using old 1.8 format protocol conventions are not
allowed to connect to 2.x servers. This flag should be set on all
connections since Lustre 1.8.5.

If the OBD_CONNECT_LAYOUTLOCK is set then the client supports layout
lock, which allows the server to revoke the layout of a file from
a client if the layout has changed (e.g. migration between OSTs or
changes in replication state). The server will not grant a layout
lock to the old clients that do not support this feature.

If the OBD_CONNECT_64BITHASH is set then the client supports 64-bit
directory 'readdir' cookie. The server will also use 64-bit hash mode
while working with ldiskfs.

If the OBD_CONNECT_JOBSTATS is set then the client fills jobid in
'ptlrpc_body' so server can provide extended RPC statistics per jobid.

If the OBD_CONNECT_UMASK is set then create uses client umask. This is
default flag for MDS but is not relevant for OSTs.

If the OBD_CONNECT_LVB_TYPE is set then the variable type of lock
value block (LVB) is supported by a client.  This flag was introduced
to allow the MDS to return data with an IBITS lock, in addition to
the OST object attributes returned with an EXTENT lock.

If the OBD_CONNECT_LIGHTWEIGHT is set then this connection is the
'lightweight' one. A lightweight connection has no entry in last_rcvd
file, so no recovery is possible.  A new lightweight
connection can be set up while the target is in recovery, locks can
still be acquired through this connection, although they won't be
replayed. Such type of connection is used by services like quota
manager, FLDB, etc.

If the OBD_CONNECT_PINGLESS is set then pings can be suppressed. If
the client and server have this flag during connection and the ptlrpc
module on server has the option "suppress_pings", then pings will be
suppressed for this client.  There must be an external mechanism to
notify the targets of client deaths, via the targets "evict_client"
'procfs' entries. Pings can be disabled on OSTs only.

If the OBD_CONNECT_FLOCK_DEAD is set then the client support flock
cancellation, which is used for the flock deadlock detection mechanism.

If the OBD_CONNECT_DISP_STRIPE is set then server returns a 'create
stripe' disposition for open request from the client. This helps to
optimize a recovery of open requests.

If the OBD_CONNECT_OPEN_BY_FID is set then an open by FID won't pack
the name in a request. This is used by HSM or other 'ChangeLog' consumers
for accessing objects by their FID via .lustre/fid/ instead of by name.

If the OBD_CONNECT_MDS_MDS is set then the current connection is an
intra-MDS one. Such connections are distinguished because they provide
more functionality specific to MDS-MDS interoperation such as OUT RPCs.

If the OBD_CONNECT_IMP_RECOV is set then the Imperative Recovery is
supported. Imperative recovery means the clients are notified
explicitly when and where a target has restarted after failure.

The OBD_CONNECT_REQPORTAL was used to specify that client may use
OST_REQUEST_PORTAL for requests to don't interfere with IO portal,
e.g. for MDS-OST interaction. Now it is default request portal for OSC
and this flag does nothing though it is still set on client side
during connection process.

The OBD_CONNECT_SOM flag was used to signal that MDS is capable to
store file size in file attributes, so client may get it directly from
MDS avoiding glimpse request to OSTs. This feature was implemented as
demo feature and wasn't enabled by default. Finally it was removed in
Lustre 2.7 because it causes quite complex recovery cases to handle
with relatively small benefits.

The OBD_CONNECT_QUOTA64 was used prior Lustre 2.4 for quota purposes,
it is obsoleted due to new quota design.

The OBD_CONNECT_REAL is not real connection flag but used locally on
client to distinguish real connection from local connections between
layers.

The OBD_CONNECT_CHANGE_QS was used prior Lustre 2.4 for quota, but
it is obsoleted now due to new quota design.

If the OBD_CONNECT_EINPROGRESS is set then client handles -EINPROGRESS
RPC error properly. The quota design requires that client must resend
request with -EINPROGRESS error indefinitely, until successful
completion or another error.  This flag is set on both client and
server by default. Meanwhile this flag is not checked anywhere, so does
nothing.

If the OBD_CONNECT_FLOCK_OWNER is set then 1.8 clients has fixed flock
policy and 2.x servers recognize them correctly. Meanwhile this flag
is not checked anywhere, so does nothing.

If the OBD_CONNECT_NANOSEC_TIME is set then nanosecond timestamps are
enabled.  This flag is not used yet, but reserved for future use.

If the OBD_CONNECT_SHORTIO is set then short IO feature is enabled on
server.  The server will avoid bulk IO for small amount of data but
data is encapsulated into ptlrpc request/reply. This flag is reserved
for future use and does nothing yet.