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-rw-r--r--Documentation/infiniband/user_mad.txt53
1 files changed, 40 insertions, 13 deletions
diff --git a/Documentation/infiniband/user_mad.txt b/Documentation/infiniband/user_mad.txt
index cae0c83f1ee..750fe5e80eb 100644
--- a/Documentation/infiniband/user_mad.txt
+++ b/Documentation/infiniband/user_mad.txt
@@ -28,13 +28,37 @@ Creating MAD agents
Receiving MADs
- MADs are received using read(). The buffer passed to read() must be
- large enough to hold at least one struct ib_user_mad. For example:
-
- struct ib_user_mad mad;
- ret = read(fd, &mad, sizeof mad);
- if (ret != sizeof mad)
+ MADs are received using read(). The receive side now supports
+ RMPP. The buffer passed to read() must be at least one
+ struct ib_user_mad + 256 bytes. For example:
+
+ If the buffer passed is not large enough to hold the received
+ MAD (RMPP), the errno is set to ENOSPC and the length of the
+ buffer needed is set in mad.length.
+
+ Example for normal MAD (non RMPP) reads:
+ struct ib_user_mad *mad;
+ mad = malloc(sizeof *mad + 256);
+ ret = read(fd, mad, sizeof *mad + 256);
+ if (ret != sizeof mad + 256) {
+ perror("read");
+ free(mad);
+ }
+
+ Example for RMPP reads:
+ struct ib_user_mad *mad;
+ mad = malloc(sizeof *mad + 256);
+ ret = read(fd, mad, sizeof *mad + 256);
+ if (ret == -ENOSPC)) {
+ length = mad.length;
+ free(mad);
+ mad = malloc(sizeof *mad + length);
+ ret = read(fd, mad, sizeof *mad + length);
+ }
+ if (ret < 0) {
perror("read");
+ free(mad);
+ }
In addition to the actual MAD contents, the other struct ib_user_mad
fields will be filled in with information on the received MAD. For
@@ -50,18 +74,21 @@ Sending MADs
MADs are sent using write(). The agent ID for sending should be
filled into the id field of the MAD, the destination LID should be
- filled into the lid field, and so on. For example:
+ filled into the lid field, and so on. The send side does support
+ RMPP so arbitrary length MAD can be sent. For example:
+
+ struct ib_user_mad *mad;
- struct ib_user_mad mad;
+ mad = malloc(sizeof *mad + mad_length);
- /* fill in mad.data */
+ /* fill in mad->data */
- mad.id = my_agent; /* req.id from agent registration */
- mad.lid = my_dest; /* in network byte order... */
+ mad->hdr.id = my_agent; /* req.id from agent registration */
+ mad->hdr.lid = my_dest; /* in network byte order... */
/* etc. */
- ret = write(fd, &mad, sizeof mad);
- if (ret != sizeof mad)
+ ret = write(fd, &mad, sizeof *mad + mad_length);
+ if (ret != sizeof *mad + mad_length)
perror("write");
Setting IsSM Capability Bit