pipe: add documentation and comments (0845718d) · Commits · e / devices / android_kernel_oneplus_sm7250

fs/pipe.c

+60 −1

Original line number	Diff line number	Diff line
		@@ -164,6 +164,20 @@ static void anon_pipe_buf_release(struct pipe_inode_info *pipe,
		page_cache_release(page);
		}

		/**
		* generic_pipe_buf_map - virtually map a pipe buffer
		* @pipe: the pipe that the buffer belongs to
		* @buf: the buffer that should be mapped
		* @atomic: whether to use an atomic map
		*
		* Description:
		* This function returns a kernel virtual address mapping for the
		* passed in @pipe_buffer. If @atomic is set, an atomic map is provided
		* and the caller has to be careful not to fault before calling
		* the unmap function.
		*
		* Note that this function occupies KM_USER0 if @atomic != 0.
		*/
		void generic_pipe_buf_map(struct pipe_inode_info pipe,
		struct pipe_buffer *buf, int atomic)
		{
		@@ -175,6 +189,15 @@ void generic_pipe_buf_map(struct pipe_inode_info pipe,
		return kmap(buf->page);
		}

		/**
		* generic_pipe_buf_unmap - unmap a previously mapped pipe buffer
		* @pipe: the pipe that the buffer belongs to
		* @buf: the buffer that should be unmapped
		* @map_data: the data that the mapping function returned
		*
		* Description:
		* This function undoes the mapping that ->map() provided.
		*/
		void generic_pipe_buf_unmap(struct pipe_inode_info *pipe,
		struct pipe_buffer buf, void map_data)
		{
		@@ -185,11 +208,28 @@ void generic_pipe_buf_unmap(struct pipe_inode_info *pipe,
		kunmap(buf->page);
		}

		/**
		* generic_pipe_buf_steal - attempt to take ownership of a @pipe_buffer
		* @pipe: the pipe that the buffer belongs to
		* @buf: the buffer to attempt to steal
		*
		* Description:
		* This function attempts to steal the @struct page attached to
		* @buf. If successful, this function returns 0 and returns with
		* the page locked. The caller may then reuse the page for whatever
		* he wishes, the typical use is insertion into a different file
		* page cache.
		*/
		int generic_pipe_buf_steal(struct pipe_inode_info *pipe,
		struct pipe_buffer *buf)
		{
		struct page *page = buf->page;

		/*
		* A reference of one is golden, that means that the owner of this
		* page is the only one holding a reference to it. lock the page
		* and return OK.
		*/
		if (page_count(page) == 1) {
		lock_page(page);
		return 0;
		@@ -198,11 +238,30 @@ int generic_pipe_buf_steal(struct pipe_inode_info *pipe,
		return 1;
		}

		void generic_pipe_buf_get(struct pipe_inode_info info, struct pipe_buffer buf)
		/**
		* generic_pipe_buf_get - get a reference to a @struct pipe_buffer
		* @pipe: the pipe that the buffer belongs to
		* @buf: the buffer to get a reference to
		*
		* Description:
		* This function grabs an extra reference to @buf. It's used in
		* in the tee() system call, when we duplicate the buffers in one
		* pipe into another.
		*/
		void generic_pipe_buf_get(struct pipe_inode_info pipe, struct pipe_buffer buf)
		{
		page_cache_get(buf->page);
		}

		/**
		* generic_pipe_buf_confirm - verify contents of the pipe buffer
		* @pipe: the pipe that the buffer belongs to
		* @buf: the buffer to confirm
		*
		* Description:
		* This function does nothing, because the generic pipe code uses
		* pages that are always good when inserted into the pipe.
		*/
		int generic_pipe_buf_confirm(struct pipe_inode_info *info,
		struct pipe_buffer *buf)
		{

fs/splice.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -85,6 +85,10 @@ static void page_cache_pipe_buf_release(struct pipe_inode_info *pipe,
		buf->flags &= ~PIPE_BUF_FLAG_LRU;
		}

		/*
		* Check whether the contents of buf is OK to access. Since the content
		* is a page cache page, IO may be in flight.
		*/
		static int page_cache_pipe_buf_confirm(struct pipe_inode_info *pipe,
		struct pipe_buffer *buf)
		{

include/linux/pipe_fs_i.h

+76 −1

Original line number	Diff line number	Diff line
		@@ -9,6 +9,15 @@
		#define PIPE_BUF_FLAG_ATOMIC 0x02 /* was atomically mapped */
		#define PIPE_BUF_FLAG_GIFT 0x04 /* page is a gift */

		/**
		* struct pipe_buffer - a linux kernel pipe buffer
		* @page: the page containing the data for the pipe buffer
		* @offset: offset of data inside the @page
		* @len: length of data inside the @page
		* @ops: operations associated with this buffer. See @pipe_buf_operations.
		* @flags: pipe buffer flags. See above.
		* @private: private data owned by the ops.
		**/
		struct pipe_buffer {
		struct page *page;
		unsigned int offset, len;
		@@ -17,6 +26,22 @@ struct pipe_buffer {
		unsigned long private;
		};

		/**
		* struct pipe_inode_info - a linux kernel pipe
		* @wait: reader/writer wait point in case of empty/full pipe
		* @nrbufs: the number of non-empty pipe buffers in this pipe
		* @curbuf: the current pipe buffer entry
		* @tmp_page: cached released page
		* @readers: number of current readers of this pipe
		* @writers: number of current writers of this pipe
		* @waiting_writers: number of writers blocked waiting for room
		* @r_counter: reader counter
		* @w_counter: writer counter
		* @fasync_readers: reader side fasync
		* @fasync_writers: writer side fasync
		* @inode: inode this pipe is attached to
		* @bufs: the circular array of pipe buffers
		**/
		struct pipe_inode_info {
		wait_queue_head_t wait;
		unsigned int nrbufs, curbuf;
		@@ -43,15 +68,65 @@ struct pipe_inode_info {
		* ->unmap()
		*
		* That is, ->map() must be called on a confirmed buffer,
		* same goes for ->steal().
		* same goes for ->steal(). See below for the meaning of each
		* operation. Also see kerneldoc in fs/pipe.c for the pipe
		* and generic variants of these hooks.
		*/
		struct pipe_buf_operations {
		/*
		* This is set to 1, if the generic pipe read/write may coalesce
		* data into an existing buffer. If this is set to 0, a new pipe
		* page segment is always used for new data.
		*/
		int can_merge;

		/*
		* ->map() returns a virtual address mapping of the pipe buffer.
		* The last integer flag reflects whether this should be an atomic
		* mapping or not. The atomic map is faster, however you can't take
		* page faults before calling ->unmap() again. So if you need to eg
		* access user data through copy_to/from_user(), then you must get
		* a non-atomic map. ->map() uses the KM_USER0 atomic slot for
		* atomic maps, so you can't map more than one pipe_buffer at once
		* and you have to be careful if mapping another page as source
		* or destination for a copy (IOW, it has to use something else
		* than KM_USER0).
		*/
		void * (map)(struct pipe_inode_info , struct pipe_buffer *, int);

		/*
		* Undoes ->map(), finishes the virtual mapping of the pipe buffer.
		*/
		void (unmap)(struct pipe_inode_info , struct pipe_buffer , void );

		/*
		* ->confirm() verifies that the data in the pipe buffer is there
		* and that the contents are good. If the pages in the pipe belong
		* to a file system, we may need to wait for IO completion in this
		* hook. Returns 0 for good, or a negative error value in case of
		* error.
		*/
		int (confirm)(struct pipe_inode_info , struct pipe_buffer *);

		/*
		* When the contents of this pipe buffer has been completely
		* consumed by a reader, ->release() is called.
		*/
		void (release)(struct pipe_inode_info , struct pipe_buffer *);

		/*
		* Attempt to take ownership of the pipe buffer and its contents.
		* ->steal() returns 0 for success, in which case the contents
		* of the pipe (the buf->page) is locked and now completely owned
		* by the caller. The page may then be transferred to a different
		* mapping, the most often used case is insertion into different
		* file address space cache.
		*/
		int (steal)(struct pipe_inode_info , struct pipe_buffer *);

		/*
		* Get a reference to the pipe buffer.
		*/
		void (get)(struct pipe_inode_info , struct pipe_buffer *);
		};