LU-11027 doc: Add lockahead to llapi_ladvise man

Document lockahead in the llapi_ladvise man page.

Test-Parameters: trivial
Signed-off-by: Patrick Farrell <paf@cray.com>
Change-Id: Ia709611bb2751a408e3525c538daa824b365b09c
Reviewed-on: https://review.whamcloud.com/32437
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>

diff --git a/lustre/doc/llapi_ladvise.3 b/lustre/doc/llapi_ladvise.3
index 4ef508d..d755899 100644 (file)
--- a/lustre/doc/llapi_ladvise.3
+++ b/lustre/doc/llapi_ladvise.3
@@ -28,6 +28,9 @@ can modify how the advice will be processed via bitwise-or'd values:
 .B LF_ASYNC
 Client returns to userspace immediately after submitting ladvise RPCs, leaving
 server threads to handle the advices asynchronously.
+.TP
+.B LF_UNSET
+Unset/clear a previous advice (Currently only supports LU_ADVISE_LOCKNOEXPAND).
 .PP
 Each of the
 .I ladvise
@@ -58,6 +61,12 @@ Prefetch data into server cache using optimum I/O size for the server.
 .B LU_LADVISE_DONTNEED
 Clean cached data for the specified file range(s) on the server.
 .TP
+.B LU_LADVISE_LOCKAHEAD
+Request an LDLM extent lock of the given mode on the given byte range.
+.TP
+.B LU_LADVISE_NOEXPAND
+Disable extent lock expansion behavior for I/O to this file descriptor.
+.TP
 .I lla_start
 is the offset in bytes for the start of this advice.
 .TP
@@ -67,6 +76,23 @@ is the offset in bytes (non-inclusive) for the end of this advice.
 .IR lla_value1 , " lla_value2" , " lla_value3" , " lla_value4"
 additional arguments for future advice types and should be
 set to zero if not explicitly required for a given advice type.
+Advice-specific names for these fields follow.
+.TP
+.IR lla_lockahead_mode
+When using LU_ADVISE_LOCKAHEAD, the 'lla_value1' field is used to
+communicate the requested lock mode, and can be referred to as
+lla_lockahead_mode.
+.TP
+.IR lla_peradvice_flags
+When using advices which support them, the 'lla_value2' field is
+used to communicate per-advice flags and can be referred to as
+lla_peradvice_flags.  Both LF_ASYNC and LF_UNSET are supported
+as peradvice flags.
+.TP
+.IR lla_lockahead_result
+When using LU_ADVISE_LOCKAHEAD, the 'lla_value3' field is used to
+communicate the result of the request, and can be referred to as lla_lockahead_result.
+.PP
 .PP
 .B llapi_ladvise()
 forwards the advice to Lustre servers without guaranteeing how and when
@@ -86,6 +112,13 @@ that data into each client cache with
 .B fadvise()
 may not be, due to much more data being sent to the clients.
 
+LU_LADVISE_LOCKAHEAD merits a special comment. While it is possible and
+encouraged to use it directly in your application to avoid lock contention
+(primarily for writing to a single file from multiple clients), it will
+also be available in the MPI-I/O / MPICH library from ANL for use with the
+i/o aggregation mode of that library. This is intended (eventually) to be
+the primary way this feature is used.
+
 While conceptually similar to the
 .BR posix_fadvise (2)
 and Linux