diff options
Diffstat (limited to 'Documentation/target/tcmu-design.txt')
| -rw-r--r-- | Documentation/target/tcmu-design.txt | 11 |
1 files changed, 10 insertions, 1 deletions
diff --git a/Documentation/target/tcmu-design.txt b/Documentation/target/tcmu-design.txt index bef81e42788f..4cebc1ebf99a 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_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.) |