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linux-next/Documentation/scsi/scsi_fc_transport.txt
James Smart 9ef3e4a452 [SCSI] fc_transport: fix sysfs deadlock on vport delete 
When the vport attribute "delete" is used to delete the vport, sysfs
deadlocks waiting for the write to complete, which is waiting for the
sysfs teardown to complete. Moved this effort to a work_q element.

Took the opportunity to make some other cosmetic changes:
 - removed tabs in Doc file - replaced with expanded spaces
 - minor copyright text and author text updates
 - removed a bunch of trailing whitespace

Signed-off-by: James Smart <James.Smart@emulex.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>
2007-05-26 11:47:58 -05:00

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SCSI FC Tansport
=============================================
Date: 4/12/2007
Kernel Revisions for features:
rports : <<TBS>>
vports : 2.6.22 (? TBD)
Introduction
============
This file documents the features and components of the SCSI FC Transport.
It also provides documents the API between the transport and FC LLDDs.
The FC transport can be found at:
drivers/scsi/scsi_transport_fc.c
include/scsi/scsi_transport_fc.h
include/scsi/scsi_netlink_fc.h
This file is found at Documentation/scsi/scsi_fc_transport.txt
FC Remote Ports (rports)
========================================================================
<< To Be Supplied >>
FC Virtual Ports (vports)
========================================================================
Overview:
-------------------------------
New FC standards have defined mechanisms which allows for a single physical
port to appear on as multiple communication ports. Using the N_Port Id
Virtualization (NPIV) mechanism, a point-to-point connection to a Fabric
can be assigned more than 1 N_Port_ID. Each N_Port_ID appears as a
separate port to other endpoints on the fabric, even though it shares one
physical link to the switch for communication. Each N_Port_ID can have a
unique view of the fabric based on fabric zoning and array lun-masking
(just like a normal non-NPIV adapter). Using the Virtual Fabric (VF)
mechanism, adding a fabric header to each frame allows the port to
interact with the Fabric Port to join multiple fabrics. The port will
obtain an N_Port_ID on each fabric it joins. Each fabric will have its
own unique view of endpoints and configuration parameters. NPIV may be
used together with VF so that the port can obtain multiple N_Port_IDs
on each virtual fabric.
The FC transport is now recognizing a new object - a vport. A vport is
an entity that has a world-wide unique World Wide Port Name (wwpn) and
World Wide Node Name (wwnn). The transport also allows for the FC4's to
be specified for the vport, with FCP_Initiator being the primary role
expected. Once instantiated by one of the above methods, it will have a
distinct N_Port_ID and view of fabric endpoints and storage entities.
The fc_host associated with the physical adapter will export the ability
to create vports. The transport will create the vport object within the
Linux device tree, and instruct the fc_host's driver to instantiate the
virtual port. Typically, the driver will create a new scsi_host instance
on the vport, resulting in a unique <H,C,T,L> namespace for the vport.
Thus, whether a FC port is based on a physical port or on a virtual port,
each will appear as a unique scsi_host with its own target and lun space.
Note: At this time, the transport is written to create only NPIV-based
vports. However, consideration was given to VF-based vports and it
should be a minor change to add support if needed. The remaining
discussion will concentrate on NPIV.
Note: World Wide Name assignment (and uniqueness guarantees) are left
up to an administrative entity controling the vport. For example,
if vports are to be associated with virtual machines, a XEN mgmt
utility would be responsible for creating wwpn/wwnn's for the vport,
using it's own naming authority and OUI. (Note: it already does this
for virtual MAC addresses).
Device Trees and Vport Objects:
-------------------------------
Today, the device tree typically contains the scsi_host object,
with rports and scsi target objects underneath it. Currently the FC
transport creates the vport object and places it under the scsi_host
object corresponding to the physical adapter. The LLDD will allocate
a new scsi_host for the vport and link it's object under the vport.
The remainder of the tree under the vports scsi_host is the same
as the non-NPIV case. The transport is written currently to easily
allow the parent of the vport to be something other than the scsi_host.
This could be used in the future to link the object onto a vm-specific
device tree. If the vport's parent is not the physical port's scsi_host,
a symbolic link to the vport object will be placed in the physical
port's scsi_host.
Here's what to expect in the device tree :
The typical Physical Port's Scsi_Host:
/sys/devices/.../host17/
and it has the typical decendent tree:
/sys/devices/.../host17/rport-17:0-0/target17:0:0/17:0:0:0:
and then the vport is created on the Physical Port:
/sys/devices/.../host17/vport-17:0-0
and the vport's Scsi_Host is then created:
/sys/devices/.../host17/vport-17:0-0/host18
and then the rest of the tree progresses, such as:
/sys/devices/.../host17/vport-17:0-0/host18/rport-18:0-0/target18:0:0/18:0:0:0:
Here's what to expect in the sysfs tree :
scsi_hosts:
/sys/class/scsi_host/host17 physical port's scsi_host
/sys/class/scsi_host/host18 vport's scsi_host
fc_hosts:
/sys/class/fc_host/host17 physical port's fc_host
/sys/class/fc_host/host18 vport's fc_host
fc_vports:
/sys/class/fc_vports/vport-17:0-0 the vport's fc_vport
fc_rports:
/sys/class/fc_remote_ports/rport-17:0-0 rport on the physical port
/sys/class/fc_remote_ports/rport-18:0-0 rport on the vport
Vport Attributes:
-------------------------------
The new fc_vport class object has the following attributes
node_name: Read_Only
The WWNN of the vport
port_name: Read_Only
The WWPN of the vport
roles: Read_Only
Indicates the FC4 roles enabled on the vport.
symbolic_name: Read_Write
A string, appended to the driver's symbolic port name string, which
is registered with the switch to identify the vport. For example,
a hypervisor could set this string to "Xen Domain 2 VM 5 Vport 2",
and this set of identifiers can be seen on switch management screens
to identify the port.
vport_delete: Write_Only
When written with a "1", will tear down the vport.
vport_disable: Write_Only
When written with a "1", will transition the vport to a disabled.
state. The vport will still be instantiated with the Linux kernel,
but it will not be active on the FC link.
When written with a "0", will enable the vport.
vport_last_state: Read_Only
Indicates the previous state of the vport. See the section below on
"Vport States".
vport_state: Read_Only
Indicates the state of the vport. See the section below on
"Vport States".
vport_type: Read_Only
Reflects the FC mechanism used to create the virtual port.
Only NPIV is supported currently.
For the fc_host class object, the following attributes are added for vports:
max_npiv_vports: Read_Only
Indicates the maximum number of NPIV-based vports that the
driver/adapter can support on the fc_host.
npiv_vports_inuse: Read_Only
Indicates how many NPIV-based vports have been instantiated on the
fc_host.
vport_create: Write_Only
A "simple" create interface to instantiate a vport on an fc_host.
A "<WWPN>:<WWNN>" string is written to the attribute. The transport
then instantiates the vport object and calls the LLDD to create the
vport with the role of FCP_Initiator. Each WWN is specified as 16
hex characters and may *not* contain any prefixes (e.g. 0x, x, etc).
vport_delete: Write_Only
A "simple" delete interface to teardown a vport. A "<WWPN>:<WWNN>"
string is written to the attribute. The transport will locate the
vport on the fc_host with the same WWNs and tear it down. Each WWN
is specified as 16 hex characters and may *not* contain any prefixes
(e.g. 0x, x, etc).
Vport States:
-------------------------------
Vport instantiation consists of two parts:
- Creation with the kernel and LLDD. This means all transport and
driver data structures are built up, and device objects created.
This is equivalent to a driver "attach" on an adapter, which is
independent of the adapter's link state.
- Instantiation of the vport on the FC link via ELS traffic, etc.
This is equivalent to a "link up" and successfull link initialization.
Futher information can be found in the interfaces section below for
Vport Creation.
Once a vport has been instantiated with the kernel/LLDD, a vport state
can be reported via the sysfs attribute. The following states exist:
FC_VPORT_UNKNOWN - Unknown
An temporary state, typically set only while the vport is being
instantiated with the kernel and LLDD.
FC_VPORT_ACTIVE - Active
The vport has been successfully been created on the FC link.
It is fully functional.
FC_VPORT_DISABLED - Disabled
The vport instantiated, but "disabled". The vport is not instantiated
on the FC link. This is equivalent to a physical port with the
link "down".
FC_VPORT_LINKDOWN - Linkdown
The vport is not operational as the physical link is not operational.
FC_VPORT_INITIALIZING - Initializing
The vport is in the process of instantiating on the FC link.
The LLDD will set this state just prior to starting the ELS traffic
to create the vport. This state will persist until the vport is
successfully created (state becomes FC_VPORT_ACTIVE) or it fails
(state is one of the values below). As this state is transitory,
it will not be preserved in the "vport_last_state".
FC_VPORT_NO_FABRIC_SUPP - No Fabric Support
The vport is not operational. One of the following conditions were
encountered:
- The FC topology is not Point-to-Point
- The FC port is not connected to an F_Port
- The F_Port has indicated that NPIV is not supported.
FC_VPORT_NO_FABRIC_RSCS - No Fabric Resources
The vport is not operational. The Fabric failed FDISC with a status
indicating that it does not have sufficient resources to complete
the operation.
FC_VPORT_FABRIC_LOGOUT - Fabric Logout
The vport is not operational. The Fabric has LOGO'd the N_Port_ID
associated with the vport.
FC_VPORT_FABRIC_REJ_WWN - Fabric Rejected WWN
The vport is not operational. The Fabric failed FDISC with a status
indicating that the WWN's are not valid.
FC_VPORT_FAILED - VPort Failed
The vport is not operational. This is a catchall for all other
error conditions.
The following state table indicates the different state transitions:
State Event New State
--------------------------------------------------------------------
n/a Initialization Unknown
Unknown: Link Down Linkdown
Link Up & Loop No Fabric Support
Link Up & no Fabric No Fabric Support
Link Up & FLOGI response No Fabric Support
indicates no NPIV support
Link Up & FDISC being sent Initializing
Disable request Disable
Linkdown: Link Up Unknown
Initializing: FDISC ACC Active
FDISC LS_RJT w/ no resources No Fabric Resources
FDISC LS_RJT w/ invalid Fabric Rejected WWN
pname or invalid nport_id
FDISC LS_RJT failed for Vport Failed
other reasons
Link Down Linkdown
Disable request Disable
Disable: Enable request Unknown
Active: LOGO received from fabric Fabric Logout
Link Down Linkdown
Disable request Disable
Fabric Logout: Link still up Unknown
The following 4 error states all have the same transitions:
No Fabric Support:
No Fabric Resources:
Fabric Rejected WWN:
Vport Failed:
Disable request Disable
Link goes down Linkdown
Transport <-> LLDD Interfaces :
-------------------------------
Vport support by LLDD:
The LLDD indicates support for vports by supplying a vport_create()
function in the transport template. The presense of this function will
cause the creation of the new attributes on the fc_host. As part of
the physical port completing its initialization relative to the
transport, it should set the max_npiv_vports attribute to indicate the
maximum number of vports the driver and/or adapter supports.
Vport Creation:
The LLDD vport_create() syntax is:
int vport_create(struct fc_vport *vport, bool disable)
where:
vport: Is the newly allocated vport object
disable: If "true", the vport is to be created in a disabled stated.
If "false", the vport is to be enabled upon creation.
When a request is made to create a new vport (via sgio/netlink, or the
vport_create fc_host attribute), the transport will validate that the LLDD
can support another vport (e.g. max_npiv_vports > npiv_vports_inuse).
If not, the create request will be failed. If space remains, the transport
will increment the vport count, create the vport object, and then call the
LLDD's vport_create() function with the newly allocated vport object.
As mentioned above, vport creation is divided into two parts:
- Creation with the kernel and LLDD. This means all transport and
driver data structures are built up, and device objects created.
This is equivalent to a driver "attach" on an adapter, which is
independent of the adapter's link state.
- Instantiation of the vport on the FC link via ELS traffic, etc.
This is equivalent to a "link up" and successfull link initialization.
The LLDD's vport_create() function will not synchronously wait for both
parts to be fully completed before returning. It must validate that the
infrastructure exists to support NPIV, and complete the first part of
vport creation (data structure build up) before returning. We do not
hinge vport_create() on the link-side operation mainly because:
- The link may be down. It is not a failure if it is. It simply
means the vport is in an inoperable state until the link comes up.
This is consistent with the link bouncing post vport creation.
- The vport may be created in a disabled state.
- This is consistent with a model where: the vport equates to a
FC adapter. The vport_create is synonymous with driver attachment
to the adapter, which is independent of link state.
Note: special error codes have been defined to delineate infrastructure
failure cases for quicker resolution.
The expected behavior for the LLDD's vport_create() function is:
- Validate Infrastructure:
- If the driver or adapter cannot support another vport, whether
due to improper firmware, (a lie about) max_npiv, or a lack of
some other resource - return VPCERR_UNSUPPORTED.
- If the driver validates the WWN's against those already active on
the adapter and detects an overlap - return VPCERR_BAD_WWN.
- If the driver detects the topology is loop, non-fabric, or the
FLOGI did not support NPIV - return VPCERR_NO_FABRIC_SUPP.
- Allocate data structures. If errors are encountered, such as out
of memory conditions, return the respective negative Exxx error code.
- If the role is FCP Initiator, the LLDD is to :
- Call scsi_host_alloc() to allocate a scsi_host for the vport.
- Call scsi_add_host(new_shost, &vport->dev) to start the scsi_host
and bind it as a child of the vport device.
- Initializes the fc_host attribute values.
- Kick of further vport state transitions based on the disable flag and
link state - and return success (zero).
LLDD Implementers Notes:
- It is suggested that there be a different fc_function_templates for
the physical port and the virtual port. The physical port's template
would have the vport_create, vport_delete, and vport_disable functions,
while the vports would not.
- It is suggested that there be different scsi_host_templates
for the physical port and virtual port. Likely, there are driver
attributes, embedded into the scsi_host_template, that are applicable
for the physical port only (link speed, topology setting, etc). This
ensures that the attributes are applicable to the respective scsi_host.
Vport Disable/Enable:
The LLDD vport_disable() syntax is:
int vport_disable(struct fc_vport *vport, bool disable)
where:
vport: Is vport to to be enabled or disabled
disable: If "true", the vport is to be disabled.
If "false", the vport is to be enabled.
When a request is made to change the disabled state on a vport, the
transport will validate the request against the existing vport state.
If the request is to disable and the vport is already disabled, the
request will fail. Similarly, if the request is to enable, and the
vport is not in a disabled state, the request will fail. If the request
is valid for the vport state, the transport will call the LLDD to
change the vport's state.
Within the LLDD, if a vport is disabled, it remains instantiated with
the kernel and LLDD, but it is not active or visible on the FC link in
any way. (see Vport Creation and the 2 part instantiation discussion).
The vport will remain in this state until it is deleted or re-enabled.
When enabling a vport, the LLDD reinstantiates the vport on the FC
link - essentially restarting the LLDD statemachine (see Vport States
above).
Vport Deletion:
The LLDD vport_delete() syntax is:
int vport_delete(struct fc_vport *vport)
where:
vport: Is vport to delete
When a request is made to delete a vport (via sgio/netlink, or via the
fc_host or fc_vport vport_delete attributes), the transport will call
the LLDD to terminate the vport on the FC link, and teardown all other
datastructures and references. If the LLDD completes successfully,
the transport will teardown the vport objects and complete the vport
removal. If the LLDD delete request fails, the vport object will remain,
but will be in an indeterminate state.
Within the LLDD, the normal code paths for a scsi_host teardown should
be followed. E.g. If the vport has a FCP Initiator role, the LLDD
will call fc_remove_host() for the vports scsi_host, followed by
scsi_remove_host() and scsi_host_put() for the vports scsi_host.
Other:
fc_host port_type attribute:
There is a new fc_host port_type value - FC_PORTTYPE_NPIV. This value
must be set on all vport-based fc_hosts. Normally, on a physical port,
the port_type attribute would be set to NPORT, NLPORT, etc based on the
topology type and existence of the fabric. As this is not applicable to
a vport, it makes more sense to report the FC mechanism used to create
the vport.
Driver unload:
FC drivers are required to call fc_remove_host() prior to calling
scsi_remove_host(). This allows the fc_host to tear down all remote
ports prior the scsi_host being torn down. The fc_remove_host() call
was updated to remove all vports for the fc_host as well.
Credits
=======
The following people have contributed to this document:
James Smart
james.smart@emulex.com
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