tjh.dev
Linux kernel mirror (for testing)
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kernel
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linux
1USERSPACE MAD ACCESS
2
3Device files
4
5 Each port of each InfiniBand device has a "umad" device and an
6 "issm" device attached. For example, a two-port HCA will have two
7 umad devices and two issm devices, while a switch will have one
8 device of each type (for switch port 0).
9
10Creating MAD agents
11
12 A MAD agent can be created by filling in a struct ib_user_mad_reg_req
13 and then calling the IB_USER_MAD_REGISTER_AGENT ioctl on a file
14 descriptor for the appropriate device file. If the registration
15 request succeeds, a 32-bit id will be returned in the structure.
16 For example:
17
18 struct ib_user_mad_reg_req req = { /* ... */ };
19 ret = ioctl(fd, IB_USER_MAD_REGISTER_AGENT, (char *) &req);
20 if (!ret)
21 my_agent = req.id;
22 else
23 perror("agent register");
24
25 Agents can be unregistered with the IB_USER_MAD_UNREGISTER_AGENT
26 ioctl. Also, all agents registered through a file descriptor will
27 be unregistered when the descriptor is closed.
28
29Receiving MADs
30
31 MADs are received using read(). The receive side now supports
32 RMPP. The buffer passed to read() must be at least one
33 struct ib_user_mad + 256 bytes. For example:
34
35 If the buffer passed is not large enough to hold the received
36 MAD (RMPP), the errno is set to ENOSPC and the length of the
37 buffer needed is set in mad.length.
38
39 Example for normal MAD (non RMPP) reads:
40 struct ib_user_mad *mad;
41 mad = malloc(sizeof *mad + 256);
42 ret = read(fd, mad, sizeof *mad + 256);
43 if (ret != sizeof mad + 256) {
44 perror("read");
45 free(mad);
46 }
47
48 Example for RMPP reads:
49 struct ib_user_mad *mad;
50 mad = malloc(sizeof *mad + 256);
51 ret = read(fd, mad, sizeof *mad + 256);
52 if (ret == -ENOSPC)) {
53 length = mad.length;
54 free(mad);
55 mad = malloc(sizeof *mad + length);
56 ret = read(fd, mad, sizeof *mad + length);
57 }
58 if (ret < 0) {
59 perror("read");
60 free(mad);
61 }
62
63 In addition to the actual MAD contents, the other struct ib_user_mad
64 fields will be filled in with information on the received MAD. For
65 example, the remote LID will be in mad.lid.
66
67 If a send times out, a receive will be generated with mad.status set
68 to ETIMEDOUT. Otherwise when a MAD has been successfully received,
69 mad.status will be 0.
70
71 poll()/select() may be used to wait until a MAD can be read.
72
73Sending MADs
74
75 MADs are sent using write(). The agent ID for sending should be
76 filled into the id field of the MAD, the destination LID should be
77 filled into the lid field, and so on. The send side does support
78 RMPP so arbitrary length MAD can be sent. For example:
79
80 struct ib_user_mad *mad;
81
82 mad = malloc(sizeof *mad + mad_length);
83
84 /* fill in mad->data */
85
86 mad->hdr.id = my_agent; /* req.id from agent registration */
87 mad->hdr.lid = my_dest; /* in network byte order... */
88 /* etc. */
89
90 ret = write(fd, &mad, sizeof *mad + mad_length);
91 if (ret != sizeof *mad + mad_length)
92 perror("write");
93
94Setting IsSM Capability Bit
95
96 To set the IsSM capability bit for a port, simply open the
97 corresponding issm device file. If the IsSM bit is already set,
98 then the open call will block until the bit is cleared (or return
99 immediately with errno set to EAGAIN if the O_NONBLOCK flag is
100 passed to open()). The IsSM bit will be cleared when the issm file
101 is closed. No read, write or other operations can be performed on
102 the issm file.
103
104/dev files
105
106 To create the appropriate character device files automatically with
107 udev, a rule like
108
109 KERNEL="umad*", NAME="infiniband/%k"
110 KERNEL="issm*", NAME="infiniband/%k"
111
112 can be used. This will create device nodes named
113
114 /dev/infiniband/umad0
115 /dev/infiniband/issm0
116
117 for the first port, and so on. The InfiniBand device and port
118 associated with these devices can be determined from the files
119
120 /sys/class/infiniband_mad/umad0/ibdev
121 /sys/class/infiniband_mad/umad0/port
122
123 and
124
125 /sys/class/infiniband_mad/issm0/ibdev
126 /sys/class/infiniband_mad/issm0/port