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-rw-r--r--Documentation/filesystems/relayfs.txt57
1 files changed, 34 insertions, 23 deletions
diff --git a/Documentation/filesystems/relayfs.txt b/Documentation/filesystems/relayfs.txt
index d9693cb8602e..5832377b7340 100644
--- a/Documentation/filesystems/relayfs.txt
+++ b/Documentation/filesystems/relayfs.txt
@@ -44,30 +44,41 @@ relayfs can operate in a mode where it will overwrite data not yet
44collected by userspace, and not wait for it to consume it. 44collected by userspace, and not wait for it to consume it.
45 45
46relayfs itself does not provide for communication of such data between 46relayfs itself does not provide for communication of such data between
47userspace and kernel, allowing the kernel side to remain simple and not 47userspace and kernel, allowing the kernel side to remain simple and
48impose a single interface on userspace. It does provide a separate 48not impose a single interface on userspace. It does provide a set of
49helper though, described below. 49examples and a separate helper though, described below.
50
51klog and relay-apps example code
52================================
53
54relayfs itself is ready to use, but to make things easier, a couple
55simple utility functions and a set of examples are provided.
56
57The relay-apps example tarball, available on the relayfs sourceforge
58site, contains a set of self-contained examples, each consisting of a
59pair of .c files containing boilerplate code for each of the user and
60kernel sides of a relayfs application; combined these two sets of
61boilerplate code provide glue to easily stream data to disk, without
62having to bother with mundane housekeeping chores.
63
64The 'klog debugging functions' patch (klog.patch in the relay-apps
65tarball) provides a couple of high-level logging functions to the
66kernel which allow writing formatted text or raw data to a channel,
67regardless of whether a channel to write into exists or not, or
68whether relayfs is compiled into the kernel or is configured as a
69module. These functions allow you to put unconditional 'trace'
70statements anywhere in the kernel or kernel modules; only when there
71is a 'klog handler' registered will data actually be logged (see the
72klog and kleak examples for details).
73
74It is of course possible to use relayfs from scratch i.e. without
75using any of the relay-apps example code or klog, but you'll have to
76implement communication between userspace and kernel, allowing both to
77convey the state of buffers (full, empty, amount of padding).
78
79klog and the relay-apps examples can be found in the relay-apps
80tarball on http://relayfs.sourceforge.net
50 81
51klog, relay-app & librelay
52==========================
53
54relayfs itself is ready to use, but to make things easier, two
55additional systems are provided. klog is a simple wrapper to make
56writing formatted text or raw data to a channel simpler, regardless of
57whether a channel to write into exists or not, or whether relayfs is
58compiled into the kernel or is configured as a module. relay-app is
59the kernel counterpart of userspace librelay.c, combined these two
60files provide glue to easily stream data to disk, without having to
61bother with housekeeping. klog and relay-app can be used together,
62with klog providing high-level logging functions to the kernel and
63relay-app taking care of kernel-user control and disk-logging chores.
64
65It is possible to use relayfs without relay-app & librelay, but you'll
66have to implement communication between userspace and kernel, allowing
67both to convey the state of buffers (full, empty, amount of padding).
68
69klog, relay-app and librelay can be found in the relay-apps tarball on
70http://relayfs.sourceforge.net
71 82
72The relayfs user space API 83The relayfs user space API
73========================== 84==========================