diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/filesystems/relayfs.txt | 57 |
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 collected by userspace, and not wait for it to consume it. relayfs itself does not provide for communication of such data between -userspace and kernel, allowing the kernel side to remain simple and not -impose a single interface on userspace. It does provide a separate -helper though, described below. +userspace and kernel, allowing the kernel side to remain simple and +not impose a single interface on userspace. It does provide a set of +examples and a separate helper though, described below. + +klog and relay-apps example code +================================ + +relayfs itself is ready to use, but to make things easier, a couple +simple utility functions and a set of examples are provided. + +The relay-apps example tarball, available on the relayfs sourceforge +site, contains a set of self-contained examples, each consisting of a +pair of .c files containing boilerplate code for each of the user and +kernel sides of a relayfs application; combined these two sets of +boilerplate code provide glue to easily stream data to disk, without +having to bother with mundane housekeeping chores. + +The 'klog debugging functions' patch (klog.patch in the relay-apps +tarball) provides a couple of high-level logging functions to the +kernel which allow writing formatted text or raw data to a channel, +regardless of whether a channel to write into exists or not, or +whether relayfs is compiled into the kernel or is configured as a +module. These functions allow you to put unconditional 'trace' +statements anywhere in the kernel or kernel modules; only when there +is a 'klog handler' registered will data actually be logged (see the +klog and kleak examples for details). + +It is of course possible to use relayfs from scratch i.e. without +using any of the relay-apps example code or klog, but you'll have to +implement communication between userspace and kernel, allowing both to +convey the state of buffers (full, empty, amount of padding). + +klog and the relay-apps examples can be found in the relay-apps +tarball on http://relayfs.sourceforge.net -klog, relay-app & librelay -========================== - -relayfs itself is ready to use, but to make things easier, two -additional systems are provided. klog is a simple wrapper to make -writing formatted text or raw data to a channel simpler, regardless of -whether a channel to write into exists or not, or whether relayfs is -compiled into the kernel or is configured as a module. relay-app is -the kernel counterpart of userspace librelay.c, combined these two -files provide glue to easily stream data to disk, without having to -bother with housekeeping. klog and relay-app can be used together, -with klog providing high-level logging functions to the kernel and -relay-app taking care of kernel-user control and disk-logging chores. - -It is possible to use relayfs without relay-app & librelay, but you'll -have to implement communication between userspace and kernel, allowing -both to convey the state of buffers (full, empty, amount of padding). - -klog, relay-app and librelay can be found in the relay-apps tarball on -http://relayfs.sourceforge.net The relayfs user space API ========================== |