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Diffstat (limited to 'Documentation/filesystems/relay.rst')
| -rw-r--r-- | Documentation/filesystems/relay.rst | 26 |
1 files changed, 13 insertions, 13 deletions
diff --git a/Documentation/filesystems/relay.rst b/Documentation/filesystems/relay.rst index 04ad083cfe62..46447dbc75ad 100644 --- a/Documentation/filesystems/relay.rst +++ b/Documentation/filesystems/relay.rst @@ -32,7 +32,7 @@ functions in the relay interface code - please see that for details. Semantics ========= -Each relay channel has one buffer per CPU, each buffer has one or more +Each relay channel has one buffer per CPU; each buffer has one or more sub-buffers. Messages are written to the first sub-buffer until it is too full to contain a new message, in which case it is written to the next (if available). Messages are never split across sub-buffers. @@ -40,7 +40,7 @@ At this point, userspace can be notified so it empties the first sub-buffer, while the kernel continues writing to the next. When notified that a sub-buffer is full, the kernel knows how many -bytes of it are padding i.e. unused space occurring because a complete +bytes of it are padding, i.e., unused space occurring because a complete message couldn't fit into a sub-buffer. Userspace can use this knowledge to copy only valid data. @@ -71,7 +71,7 @@ klog and relay-apps example code ================================ The relay interface itself is ready to use, but to make things easier, -a couple simple utility functions and a set of examples are provided. +a couple of simple utility functions and a set of examples are provided. The relay-apps example tarball, available on the relay sourceforge site, contains a set of self-contained examples, each consisting of a @@ -91,7 +91,7 @@ registered will data actually be logged (see the klog and kleak examples for details). It is of course possible to use the relay interface from scratch, -i.e. without using any of the relay-apps example code or klog, but +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). The read() interface both removes padding and internally @@ -119,7 +119,7 @@ mmap() results in channel buffer being mapped into the caller's must map the entire file, which is NRBUF * SUBBUFSIZE. read() read the contents of a channel buffer. The bytes read are - 'consumed' by the reader, i.e. they won't be available + 'consumed' by the reader, i.e., they won't be available again to subsequent reads. If the channel is being used in no-overwrite mode (the default), it can be read at any time even if there's an active kernel writer. If the @@ -138,7 +138,7 @@ poll() POLLIN/POLLRDNORM/POLLERR supported. User applications are notified when sub-buffer boundaries are crossed. close() decrements the channel buffer's refcount. When the refcount - reaches 0, i.e. when no process or kernel client has the + reaches 0, i.e., when no process or kernel client has the buffer open, the channel buffer is freed. =========== ============================================================ @@ -149,7 +149,7 @@ host filesystem must be mounted. For example:: .. Note:: - the host filesystem doesn't need to be mounted for kernel + The host filesystem doesn't need to be mounted for kernel clients to create or use channels - it only needs to be mounted when user space applications need access to the buffer data. @@ -325,7 +325,7 @@ section, as it pertains mainly to mmap() implementations. In 'overwrite' mode, also known as 'flight recorder' mode, writes continuously cycle around the buffer and will never fail, but will unconditionally overwrite old data regardless of whether it's actually -been consumed. In no-overwrite mode, writes will fail, i.e. data will +been consumed. In no-overwrite mode, writes will fail, i.e., data will be lost, if the number of unconsumed sub-buffers equals the total number of sub-buffers in the channel. It should be clear that if there is no consumer or if the consumer can't consume sub-buffers fast @@ -344,7 +344,7 @@ initialize the next sub-buffer if appropriate 2) finalize the previous sub-buffer if appropriate and 3) return a boolean value indicating whether or not to actually move on to the next sub-buffer. -To implement 'no-overwrite' mode, the userspace client would provide +To implement 'no-overwrite' mode, the userspace client provides an implementation of the subbuf_start() callback something like the following:: @@ -364,9 +364,9 @@ following:: return 1; } -If the current buffer is full, i.e. all sub-buffers remain unconsumed, +If the current buffer is full, i.e., all sub-buffers remain unconsumed, the callback returns 0 to indicate that the buffer switch should not -occur yet, i.e. until the consumer has had a chance to read the +occur yet, i.e., until the consumer has had a chance to read the current set of ready sub-buffers. For the relay_buf_full() function to make sense, the consumer is responsible for notifying the relay interface when sub-buffers have been consumed via @@ -400,7 +400,7 @@ consulted. The default subbuf_start() implementation, used if the client doesn't define any callbacks, or doesn't define the subbuf_start() callback, -implements the simplest possible 'no-overwrite' mode, i.e. it does +implements the simplest possible 'no-overwrite' mode, i.e., it does nothing but return 0. Header information can be reserved at the beginning of each sub-buffer @@ -467,7 +467,7 @@ rather than open and close a new channel for each use. relay_reset() can be used for this purpose - it resets a channel to its initial state without reallocating channel buffer memory or destroying existing mappings. It should however only be called when it's safe to -do so, i.e. when the channel isn't currently being written to. +do so, i.e., when the channel isn't currently being written to. Finally, there are a couple of utility callbacks that can be used for different purposes. buf_mapped() is called whenever a channel buffer |