target/user: Report capability of handling out-of-order completions to userspace

TCMU_MAILBOX_FLAG_CAP_OOOC was introduced, and userspace can check the flag
for out-of-order completion capability support.

Also update the document on how to use the feature.

Signed-off-by: Sheng Yang <sheng@yasker.org>
Reviewed-by: Andy Grover <agrover@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
This commit is contained in:
Sheng Yang 2016-02-29 16:02:15 -08:00 committed by Nicholas Bellinger
parent 0241fd39ce
commit 32c76de346
3 changed files with 12 additions and 1 deletions

View file

@ -117,7 +117,9 @@ userspace (respectively) to put commands on the ring, and indicate
when the commands are completed.
version - 1 (userspace should abort if otherwise)
flags - none yet defined.
flags:
- TCMU_MAILBOX_FLAG_CAP_OOOC: indicates out-of-order completion is
supported. See "The Command Ring" for details.
cmdr_off - The offset of the start of the command ring from the start
of the memory region, to account for the mailbox size.
cmdr_size - The size of the command ring. This does *not* need to be a
@ -162,6 +164,13 @@ rsp.sense_buffer if necessary. Userspace then increments
mailbox.cmd_tail by entry.hdr.length (mod cmdr_size) and signals the
kernel via the UIO method, a 4-byte write to the file descriptor.
If TCMU_MAILBOX_FLAG_CAP_OOOC is set for mailbox->flags, kernel is
capable of handling out-of-order completions. In this case, userspace can
handle command in different order other than original. Since kernel would
still process the commands in the same order it appeared in the command
ring, userspace need to update the cmd->id when completing the
command(a.k.a steal the original command's entry).
When the opcode is PAD, userspace only updates cmd_tail as above --
it's a no-op. (The kernel inserts PAD entries to ensure each CMD entry
is contiguous within the command ring.)

View file

@ -930,6 +930,7 @@ static int tcmu_configure_device(struct se_device *dev)
mb = udev->mb_addr;
mb->version = TCMU_MAILBOX_VERSION;
mb->flags = TCMU_MAILBOX_FLAG_CAP_OOOC;
mb->cmdr_off = CMDR_OFF;
mb->cmdr_size = udev->cmdr_size;

View file

@ -41,6 +41,7 @@
#define TCMU_MAILBOX_VERSION 2
#define ALIGN_SIZE 64 /* Should be enough for most CPUs */
#define TCMU_MAILBOX_FLAG_CAP_OOOC (1 << 0) /* Out-of-order completions */
struct tcmu_mailbox {
__u16 version;