@@ -84,5 +84,6 @@ Documentation for filesystem implementations.
proc
qnx6
ramfs-rootfs-initramfs
+ relay
virtiofs
vfat
similarity index 91%
rename from Documentation/filesystems/relay.txt
rename to Documentation/filesystems/relay.rst
@@ -1,3 +1,6 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+==================================
relay interface (formerly relayfs)
==================================
@@ -108,6 +111,7 @@ The relay interface implements basic file operations for user space
access to relay channel buffer data. Here are the file operations
that are available and some comments regarding their behavior:
+=========== ============================================================
open() enables user to open an _existing_ channel buffer.
mmap() results in channel buffer being mapped into the caller's
@@ -136,13 +140,16 @@ poll() POLLIN/POLLRDNORM/POLLERR supported. User applications are
close() decrements the channel buffer's refcount. When the refcount
reaches 0, i.e. when no process or kernel client has the
buffer open, the channel buffer is freed.
+=========== ============================================================
In order for a user application to make use of relay files, the
-host filesystem must be mounted. For example,
+host filesystem must be mounted. For example::
mount -t debugfs debugfs /sys/kernel/debug
-NOTE: the host filesystem doesn't need to be mounted for kernel
+.. Note::
+
+ 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.
@@ -154,7 +161,7 @@ The relay interface kernel API
Here's a summary of the API the relay interface provides to in-kernel clients:
TBD(curr. line MT:/API/)
- channel management functions:
+ channel management functions::
relay_open(base_filename, parent, subbuf_size, n_subbufs,
callbacks, private_data)
@@ -162,17 +169,17 @@ TBD(curr. line MT:/API/)
relay_flush(chan)
relay_reset(chan)
- channel management typically called on instigation of userspace:
+ channel management typically called on instigation of userspace::
relay_subbufs_consumed(chan, cpu, subbufs_consumed)
- write functions:
+ write functions::
relay_write(chan, data, length)
__relay_write(chan, data, length)
relay_reserve(chan, length)
- callbacks:
+ callbacks::
subbuf_start(buf, subbuf, prev_subbuf, prev_padding)
buf_mapped(buf, filp)
@@ -180,7 +187,7 @@ TBD(curr. line MT:/API/)
create_buf_file(filename, parent, mode, buf, is_global)
remove_buf_file(dentry)
- helper functions:
+ helper functions::
relay_buf_full(buf)
subbuf_start_reserve(buf, length)
@@ -215,41 +222,41 @@ the file(s) created in create_buf_file() and is called during
relay_close().
Here are some typical definitions for these callbacks, in this case
-using debugfs:
+using debugfs::
-/*
- * create_buf_file() callback. Creates relay file in debugfs.
- */
-static struct dentry *create_buf_file_handler(const char *filename,
- struct dentry *parent,
- umode_t mode,
- struct rchan_buf *buf,
- int *is_global)
-{
- return debugfs_create_file(filename, mode, parent, buf,
- &relay_file_operations);
-}
+ /*
+ * create_buf_file() callback. Creates relay file in debugfs.
+ */
+ static struct dentry *create_buf_file_handler(const char *filename,
+ struct dentry *parent,
+ umode_t mode,
+ struct rchan_buf *buf,
+ int *is_global)
+ {
+ return debugfs_create_file(filename, mode, parent, buf,
+ &relay_file_operations);
+ }
-/*
- * remove_buf_file() callback. Removes relay file from debugfs.
- */
-static int remove_buf_file_handler(struct dentry *dentry)
-{
- debugfs_remove(dentry);
+ /*
+ * remove_buf_file() callback. Removes relay file from debugfs.
+ */
+ static int remove_buf_file_handler(struct dentry *dentry)
+ {
+ debugfs_remove(dentry);
- return 0;
-}
+ return 0;
+ }
-/*
- * relay interface callbacks
- */
-static struct rchan_callbacks relay_callbacks =
-{
- .create_buf_file = create_buf_file_handler,
- .remove_buf_file = remove_buf_file_handler,
-};
+ /*
+ * relay interface callbacks
+ */
+ static struct rchan_callbacks relay_callbacks =
+ {
+ .create_buf_file = create_buf_file_handler,
+ .remove_buf_file = remove_buf_file_handler,
+ };
-And an example relay_open() invocation using them:
+And an example relay_open() invocation using them::
chan = relay_open("cpu", NULL, SUBBUF_SIZE, N_SUBBUFS, &relay_callbacks, NULL);
@@ -339,23 +346,23 @@ whether or not to actually move on to the next sub-buffer.
To implement 'no-overwrite' mode, the userspace client would provide
an implementation of the subbuf_start() callback something like the
-following:
+following::
-static int subbuf_start(struct rchan_buf *buf,
- void *subbuf,
- void *prev_subbuf,
- unsigned int prev_padding)
-{
- if (prev_subbuf)
- *((unsigned *)prev_subbuf) = prev_padding;
+ static int subbuf_start(struct rchan_buf *buf,
+ void *subbuf,
+ void *prev_subbuf,
+ unsigned int prev_padding)
+ {
+ if (prev_subbuf)
+ *((unsigned *)prev_subbuf) = prev_padding;
- if (relay_buf_full(buf))
- return 0;
+ if (relay_buf_full(buf))
+ return 0;
- subbuf_start_reserve(buf, sizeof(unsigned int));
+ subbuf_start_reserve(buf, sizeof(unsigned int));
- return 1;
-}
+ return 1;
+ }
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
@@ -370,20 +377,20 @@ ready sub-buffers will relay_buf_full() return 0, in which case the
buffer switch can continue.
The implementation of the subbuf_start() callback for 'overwrite' mode
-would be very similar:
+would be very similar::
-static int subbuf_start(struct rchan_buf *buf,
- void *subbuf,
- void *prev_subbuf,
- size_t prev_padding)
-{
- if (prev_subbuf)
- *((unsigned *)prev_subbuf) = prev_padding;
+ static int subbuf_start(struct rchan_buf *buf,
+ void *subbuf,
+ void *prev_subbuf,
+ size_t prev_padding)
+ {
+ if (prev_subbuf)
+ *((unsigned *)prev_subbuf) = prev_padding;
- subbuf_start_reserve(buf, sizeof(unsigned int));
+ subbuf_start_reserve(buf, sizeof(unsigned int));
- return 1;
-}
+ return 1;
+ }
In this case, the relay_buf_full() check is meaningless and the
callback always returns 1, causing the buffer switch to occur
- Add a SPDX header; - Adjust document title; - Some whitespace fixes and new line breaks; - Mark literal blocks as such; - Add table markups; - Use notes markups; - Add it to filesystems/index.rst. Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org> --- Documentation/filesystems/index.rst | 1 + .../filesystems/{relay.txt => relay.rst} | 129 +++++++++--------- 2 files changed, 69 insertions(+), 61 deletions(-) rename Documentation/filesystems/{relay.txt => relay.rst} (91%)