mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-09-12 05:48:40 +00:00
![Linus Torvalds](/assets/img/avatar_default.png)
This code is ancient, and goes back to when we only had a single page for the pipe buffers. The exact history is hidden in the mists of time (ie "before git", and in fact predates the BK repository too). At that long-ago point in time, it actually helped to try to merge big back-and-forth pipe reads and writes, and not limit pipe reads to the single pipe buffer in length just because that was all we had at a time. However, since then we've expanded the pipe buffers to multiple pages, and this logic really doesn't seem to make sense. And a lot of it is somewhat questionable (ie "hmm, the user asked for a non-blocking read, but we see that there's a writer pending, so let's wait anyway to get the extra data that the writer will have"). But more importantly, it makes the "go to sleep" logic much less obvious, and considering the wakeup issues we've had, I want to make for less of those kinds of things. Cc: David Howells <dhowells@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
246 lines
7.5 KiB
C
246 lines
7.5 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
|
|
#ifndef _LINUX_PIPE_FS_I_H
|
|
#define _LINUX_PIPE_FS_I_H
|
|
|
|
#define PIPE_DEF_BUFFERS 16
|
|
|
|
#define PIPE_BUF_FLAG_LRU 0x01 /* page is on the LRU */
|
|
#define PIPE_BUF_FLAG_ATOMIC 0x02 /* was atomically mapped */
|
|
#define PIPE_BUF_FLAG_GIFT 0x04 /* page is a gift */
|
|
#define PIPE_BUF_FLAG_PACKET 0x08 /* read() as a packet */
|
|
|
|
/**
|
|
* 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;
|
|
const struct pipe_buf_operations *ops;
|
|
unsigned int flags;
|
|
unsigned long private;
|
|
};
|
|
|
|
/**
|
|
* struct pipe_inode_info - a linux kernel pipe
|
|
* @mutex: mutex protecting the whole thing
|
|
* @wait: reader/writer wait point in case of empty/full pipe
|
|
* @head: The point of buffer production
|
|
* @tail: The point of buffer consumption
|
|
* @max_usage: The maximum number of slots that may be used in the ring
|
|
* @ring_size: total number of buffers (should be a power of 2)
|
|
* @tmp_page: cached released page
|
|
* @readers: number of current readers of this pipe
|
|
* @writers: number of current writers of this pipe
|
|
* @files: number of struct file referring this pipe (protected by ->i_lock)
|
|
* @r_counter: reader counter
|
|
* @w_counter: writer counter
|
|
* @fasync_readers: reader side fasync
|
|
* @fasync_writers: writer side fasync
|
|
* @bufs: the circular array of pipe buffers
|
|
* @user: the user who created this pipe
|
|
**/
|
|
struct pipe_inode_info {
|
|
struct mutex mutex;
|
|
wait_queue_head_t wait;
|
|
unsigned int head;
|
|
unsigned int tail;
|
|
unsigned int max_usage;
|
|
unsigned int ring_size;
|
|
unsigned int readers;
|
|
unsigned int writers;
|
|
unsigned int files;
|
|
unsigned int r_counter;
|
|
unsigned int w_counter;
|
|
struct page *tmp_page;
|
|
struct fasync_struct *fasync_readers;
|
|
struct fasync_struct *fasync_writers;
|
|
struct pipe_buffer *bufs;
|
|
struct user_struct *user;
|
|
};
|
|
|
|
/*
|
|
* Note on the nesting of these functions:
|
|
*
|
|
* ->confirm()
|
|
* ->steal()
|
|
*
|
|
* That is, ->steal() must be called on a confirmed buffer.
|
|
* 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 {
|
|
/*
|
|
* ->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.
|
|
*/
|
|
bool (*get)(struct pipe_inode_info *, struct pipe_buffer *);
|
|
};
|
|
|
|
/**
|
|
* pipe_empty - Return true if the pipe is empty
|
|
* @head: The pipe ring head pointer
|
|
* @tail: The pipe ring tail pointer
|
|
*/
|
|
static inline bool pipe_empty(unsigned int head, unsigned int tail)
|
|
{
|
|
return head == tail;
|
|
}
|
|
|
|
/**
|
|
* pipe_occupancy - Return number of slots used in the pipe
|
|
* @head: The pipe ring head pointer
|
|
* @tail: The pipe ring tail pointer
|
|
*/
|
|
static inline unsigned int pipe_occupancy(unsigned int head, unsigned int tail)
|
|
{
|
|
return head - tail;
|
|
}
|
|
|
|
/**
|
|
* pipe_full - Return true if the pipe is full
|
|
* @head: The pipe ring head pointer
|
|
* @tail: The pipe ring tail pointer
|
|
* @limit: The maximum amount of slots available.
|
|
*/
|
|
static inline bool pipe_full(unsigned int head, unsigned int tail,
|
|
unsigned int limit)
|
|
{
|
|
return pipe_occupancy(head, tail) >= limit;
|
|
}
|
|
|
|
/**
|
|
* pipe_space_for_user - Return number of slots available to userspace
|
|
* @head: The pipe ring head pointer
|
|
* @tail: The pipe ring tail pointer
|
|
* @pipe: The pipe info structure
|
|
*/
|
|
static inline unsigned int pipe_space_for_user(unsigned int head, unsigned int tail,
|
|
struct pipe_inode_info *pipe)
|
|
{
|
|
unsigned int p_occupancy, p_space;
|
|
|
|
p_occupancy = pipe_occupancy(head, tail);
|
|
if (p_occupancy >= pipe->max_usage)
|
|
return 0;
|
|
p_space = pipe->ring_size - p_occupancy;
|
|
if (p_space > pipe->max_usage)
|
|
p_space = pipe->max_usage;
|
|
return p_space;
|
|
}
|
|
|
|
/**
|
|
* pipe_buf_get - get a reference to a pipe_buffer
|
|
* @pipe: the pipe that the buffer belongs to
|
|
* @buf: the buffer to get a reference to
|
|
*
|
|
* Return: %true if the reference was successfully obtained.
|
|
*/
|
|
static inline __must_check bool pipe_buf_get(struct pipe_inode_info *pipe,
|
|
struct pipe_buffer *buf)
|
|
{
|
|
return buf->ops->get(pipe, buf);
|
|
}
|
|
|
|
/**
|
|
* pipe_buf_release - put a reference to a pipe_buffer
|
|
* @pipe: the pipe that the buffer belongs to
|
|
* @buf: the buffer to put a reference to
|
|
*/
|
|
static inline void pipe_buf_release(struct pipe_inode_info *pipe,
|
|
struct pipe_buffer *buf)
|
|
{
|
|
const struct pipe_buf_operations *ops = buf->ops;
|
|
|
|
buf->ops = NULL;
|
|
ops->release(pipe, buf);
|
|
}
|
|
|
|
/**
|
|
* pipe_buf_confirm - verify contents of the pipe buffer
|
|
* @pipe: the pipe that the buffer belongs to
|
|
* @buf: the buffer to confirm
|
|
*/
|
|
static inline int pipe_buf_confirm(struct pipe_inode_info *pipe,
|
|
struct pipe_buffer *buf)
|
|
{
|
|
return buf->ops->confirm(pipe, buf);
|
|
}
|
|
|
|
/**
|
|
* 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
|
|
*/
|
|
static inline int pipe_buf_steal(struct pipe_inode_info *pipe,
|
|
struct pipe_buffer *buf)
|
|
{
|
|
return buf->ops->steal(pipe, buf);
|
|
}
|
|
|
|
/* Differs from PIPE_BUF in that PIPE_SIZE is the length of the actual
|
|
memory allocation, whereas PIPE_BUF makes atomicity guarantees. */
|
|
#define PIPE_SIZE PAGE_SIZE
|
|
|
|
/* Pipe lock and unlock operations */
|
|
void pipe_lock(struct pipe_inode_info *);
|
|
void pipe_unlock(struct pipe_inode_info *);
|
|
void pipe_double_lock(struct pipe_inode_info *, struct pipe_inode_info *);
|
|
|
|
extern unsigned int pipe_max_size;
|
|
extern unsigned long pipe_user_pages_hard;
|
|
extern unsigned long pipe_user_pages_soft;
|
|
|
|
/* Drop the inode semaphore and wait for a pipe event, atomically */
|
|
void pipe_wait(struct pipe_inode_info *pipe);
|
|
|
|
struct pipe_inode_info *alloc_pipe_info(void);
|
|
void free_pipe_info(struct pipe_inode_info *);
|
|
|
|
/* Generic pipe buffer ops functions */
|
|
bool generic_pipe_buf_get(struct pipe_inode_info *, struct pipe_buffer *);
|
|
int generic_pipe_buf_confirm(struct pipe_inode_info *, struct pipe_buffer *);
|
|
int generic_pipe_buf_steal(struct pipe_inode_info *, struct pipe_buffer *);
|
|
int generic_pipe_buf_nosteal(struct pipe_inode_info *, struct pipe_buffer *);
|
|
void generic_pipe_buf_release(struct pipe_inode_info *, struct pipe_buffer *);
|
|
void pipe_buf_mark_unmergeable(struct pipe_buffer *buf);
|
|
|
|
extern const struct pipe_buf_operations nosteal_pipe_buf_ops;
|
|
|
|
/* for F_SETPIPE_SZ and F_GETPIPE_SZ */
|
|
long pipe_fcntl(struct file *, unsigned int, unsigned long arg);
|
|
struct pipe_inode_info *get_pipe_info(struct file *file);
|
|
|
|
int create_pipe_files(struct file **, int);
|
|
unsigned int round_pipe_size(unsigned long size);
|
|
|
|
#endif
|