TCMU_MAILBOX_FLAG_CAP_ASYNC was introduced, and userspace can check the flag
for async capability support.
Also update the document on how to use the feature.
---
Documentation/target/tcmu-design.txt | 11 ++++++++++-
drivers/target/target_core_user.c | 1 +
include/uapi/linux/target_core_user.h | 1 +
3 files changed, 12 insertions(+), 1 deletion(-)
diff --git a/Documentation/target/tcmu-design.txt b/Documentation/target/tcmu-design.txt
index bef81e4..9d27523 100644
--- a/Documentation/target/tcmu-design.txt
+++ b/Documentation/target/tcmu-design.txt
@@ -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_ASYNC: indicates asynchronize IO 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_ASYNC is set for mailbox->flags, kernel is
+capable of supporting asynchronized IO. 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.)
diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c
index d0655913..844a3e1 100644
--- a/drivers/target/target_core_user.c
+++ b/drivers/target/target_core_user.c
@@ -931,6 +931,7 @@ static int tcmu_configure_device(struct se_device *dev)
mb = udev->mb_addr;
mb->version = TCMU_MAILBOX_VERSION;
+ mb->flags = TCMU_MAILBOX_FLAG_CAP_ASYNC;
mb->cmdr_off = CMDR_OFF;
mb->cmdr_size = udev->cmdr_size;
diff --git a/include/uapi/linux/target_core_user.h b/include/uapi/linux/target_core_user.h
index 95c6521..09b00bb 100644
--- a/include/uapi/linux/target_core_user.h
+++ b/include/uapi/linux/target_core_user.h
@@ -41,6 +41,7 @@
#define TCMU_MAILBOX_VERSION 2
#define ALIGN_SIZE 64 /* Should be enough for most CPUs */
+#define TCMU_MAILBOX_FLAG_CAP_ASYNC (1 << 0)
struct tcmu_mailbox {
__u16 version;
--
2.1.4
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