1 ====================
2 Userspace MAD access
3 ====================
4
5 Device files
6 ============
7
8 Each port of each InfiniBand device has a "umad" device and an
9 "issm" device attached. For example, a two-port HCA will have two
10 umad devices and two issm devices, while a switch will have one
11 device of each type (for switch port 0).
12
13 Creating MAD agents
14 ===================
15
16 A MAD agent can be created by filling in a struct ib_user_mad_reg_req
17 and then calling the IB_USER_MAD_REGISTER_AGENT ioctl on a file
18 descriptor for the appropriate device file. If the registration
19 request succeeds, a 32-bit id will be returned in the structure.
20 For example::
21
22 struct ib_user_mad_reg_req req = { /* ... */ };
23 ret = ioctl(fd, IB_USER_MAD_REGISTER_AGENT, (char *) &req);
24 if (!ret)
25 my_agent = req.id;
26 else
27 perror("agent register");
28
29 Agents can be unregistered with the IB_USER_MAD_UNREGISTER_AGENT
30 ioctl. Also, all agents registered through a file descriptor will
31 be unregistered when the descriptor is closed.
32
33 2014
34 a new registration ioctl is now provided which allows additional
35 fields to be provided during registration.
36 Users of this registration call are implicitly setting the use of
37 pkey_index (see below).
38
39 Receiving MADs
40 ==============
41
42 MADs are received using read(). The receive side now supports
43 RMPP. The buffer passed to read() must be at least one
44 struct ib_user_mad + 256 bytes. For example:
45
46 If the buffer passed is not large enough to hold the received
47 MAD (RMPP), the errno is set to ENOSPC and the length of the
48 buffer needed is set in mad.length.
49
50 Example for normal MAD (non RMPP) reads::
51
52 struct ib_user_mad *mad;
53 mad = malloc(sizeof *mad + 256);
54 ret = read(fd, mad, sizeof *mad + 256);
55 if (ret != sizeof mad + 256) {
56 perror("read");
57 free(mad);
58 }
59
60 Example for RMPP reads::
61
62 struct ib_user_mad *mad;
63 mad = malloc(sizeof *mad + 256);
64 ret = read(fd, mad, sizeof *mad + 256);
65 if (ret == -ENOSPC)) {
66 length = mad.length;
67 free(mad);
68 mad = malloc(sizeof *mad + length);
69 ret = read(fd, mad, sizeof *mad + length);
70 }
71 if (ret < 0) {
72 perror("read");
73 free(mad);
74 }
75
76 In addition to the actual MAD contents, the other struct ib_user_mad
77 fields will be filled in with information on the received MAD. For
78 example, the remote LID will be in mad.lid.
79
80 If a send times out, a receive will be generated with mad.status set
81 to ETIMEDOUT. Otherwise when a MAD has been successfully received,
82 mad.status will be 0.
83
84 poll()/select() may be used to wait until a MAD can be read.
85
86 Sending MADs
87 ============
88
89 MADs are sent using write(). The agent ID for sending should be
90 filled into the id field of the MAD, the destination LID should be
91 filled into the lid field, and so on. The send side does support
92 RMPP so arbitrary length MAD can be sent. For example::
93
94 struct ib_user_mad *mad;
95
96 mad = malloc(sizeof *mad + mad_length);
97
98 /* fill in mad->data */
99
100 mad->hdr.id = my_agent; /* req.id from agent registration */
101 mad->hdr.lid = my_dest; /* in network byte order... */
102 /* etc. */
103
104 ret = write(fd, &mad, sizeof *mad + mad_length);
105 if (ret != sizeof *mad + mad_length)
106 perror("write");
107
108 Transaction IDs
109 ===============
110
111 Users of the umad devices can use the lower 32 bits of the
112 transaction ID field (that is, the least significant half of the
113 field in network byte order) in MADs being sent to match
114 request/response pairs. The upper 32 bits are reserved for use by
115 the kernel and will be overwritten before a MAD is sent.
116
117 P_Key Index Handling
118 ====================
119
120 The old ib_umad interface did not allow setting the P_Key index for
121 MADs that are sent and did not provide a way for obtaining the P_Key
122 index of received MADs. A new layout for struct ib_user_mad_hdr
123 with a pkey_index member has been defined; however, to preserve binary
124 compatibility with older applications, this new layout will not be used
125 unless one of IB_USER_MAD_ENABLE_PKEY or IB_USER_MAD_REGISTER_AGENT2 ioctl's
126 are called before a file descriptor is used for anything else.
127
128 In September 2008, the IB_USER_MAD_ABI_VERSION will be incremented
129 to 6, the new layout of struct ib_user_mad_hdr will be used by
130 default, and the IB_USER_MAD_ENABLE_PKEY ioctl will be removed.
131
132 Setting IsSM Capability Bit
133 ===========================
134
135 To set the IsSM capability bit for a port, simply open the
136 corresponding issm device file. If the IsSM bit is already set,
137 then the open call will block until the bit is cleared (or return
138 immediately with errno set to EAGAIN if the O_NONBLOCK flag is
139 passed to open()). The IsSM bit will be cleared when the issm file
140 is closed. No read, write or other operations can be performed on
141 the issm file.
142
143 /dev files
144 ==========
145
146 To create the appropriate character device files automatically with
147 udev, a rule like::
148
149 KERNEL=="umad*", NAME="infiniband/%k"
150 KERNEL=="issm*", NAME="infiniband/%k"
151
152 can be used. This will create device nodes named::
153
154 /dev/infiniband/umad0
155 /dev/infiniband/issm0
156
157 for the first port, and so on. The InfiniBand device and port
158 associated with these devices can be determined from the files::
159
160 /sys/class/infiniband_mad/umad0/ibdev
161 /sys/class/infiniband_mad/umad0/port
162
163 and::
164
165 /sys/class/infiniband_mad/issm0/ibdev
166 /sys/class/infiniband_mad/issm0/port
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