diff options
| -rw-r--r-- | Documentation/filesystems/relayfs.txt | 21 |
1 files changed, 20 insertions, 1 deletions
diff --git a/Documentation/filesystems/relayfs.txt b/Documentation/filesystems/relayfs.txt index 4221b3a52e2..d9693cb8602 100644 --- a/Documentation/filesystems/relayfs.txt +++ b/Documentation/filesystems/relayfs.txt @@ -143,7 +143,7 @@ Here's a summary of the API relayfs provides to in-kernel clients: subbuf_start(buf, subbuf, prev_subbuf, prev_padding) buf_mapped(buf, filp) buf_unmapped(buf, filp) - create_buf_file(filename, parent, mode, buf) + create_buf_file(filename, parent, mode, buf, is_global) remove_buf_file(dentry) helper functions: @@ -367,6 +367,25 @@ create_buf_file() is defined, remove_buf_file() must also be defined; it's responsible for deleting the file(s) created in create_buf_file() and is called during relay_close(). +The create_buf_file() implementation can also be defined in such a way +as to allow the creation of a single 'global' buffer instead of the +default per-cpu set. This can be useful for applications interested +mainly in seeing the relative ordering of system-wide events without +the need to bother with saving explicit timestamps for the purpose of +merging/sorting per-cpu files in a postprocessing step. + +To have relay_open() create a global buffer, the create_buf_file() +implementation should set the value of the is_global outparam to a +non-zero value in addition to creating the file that will be used to +represent the single buffer. In the case of a global buffer, +create_buf_file() and remove_buf_file() will be called only once. The +normal channel-writing functions e.g. relay_write() can still be used +- writes from any cpu will transparently end up in the global buffer - +but since it is a global buffer, callers should make sure they use the +proper locking for such a buffer, either by wrapping writes in a +spinlock, or by copying a write function from relayfs_fs.h and +creating a local version that internally does the proper locking. + See the 'exported-relayfile' examples in the relay-apps tarball for examples of creating and using relay files in debugfs. |