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scsi: target: tcmu: Add new feature KEEP_BUF

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When running command pipelining for WRITE direction commands (e.g. tape
device write), userspace sends cmd completion to cmd ring before processing
write data. In that case userspace has to copy data before sending
completion, because cmd completion also implicitly releases the data buffer
in data area.

The new feature KEEP_BUF allows userspace to optionally keep the buffer
after completion by setting new bit TCMU_UFLAG_KEEP_BUF in
tcmu_cmd_entry_hdr->uflags. In that case buffer has to be released
explicitly by writing the cmd_id to new action item free_kept_buf.

All kept buffers are released during reset_ring and if userspace closes uio
device (tcmu_release).

Link: https://lore.kernel.org/r/20210713175021.20103-1-bostroesser@gmail.com
Reviewed-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Bodo Stroesser <bostroesser@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
This commit is contained in:
Bodo Stroesser 2021-07-13 19:50:21 +02:00 • committed by Martin K. Petersen
parent c11a1ae9b8
commit 018c14911d
2 changed files with 141 additions and 11 deletions
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2
include/uapi/linux/target_core_user.h
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@ -46,6 +46,7 @@
#define TCMU_MAILBOX_FLAG_CAP_OOOC (1 << 0) /* Out-of-order completions */
#define TCMU_MAILBOX_FLAG_CAP_READ_LEN (1 << 1) /* Read data length */
#define TCMU_MAILBOX_FLAG_CAP_TMR (1 << 2) /* TMR notifications */
#define TCMU_MAILBOX_FLAG_CAP_KEEP_BUF (1<<3) /* Keep buf after cmd completion */
struct tcmu_mailbox {
__u16 version;
@ -75,6 +76,7 @@ struct tcmu_cmd_entry_hdr {
__u8 kflags;
#define TCMU_UFLAG_UNKNOWN_OP 0x1
#define TCMU_UFLAG_READ_LEN 0x2
#define TCMU_UFLAG_KEEP_BUF 0x4
__u8 uflags;
} __packed;