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MAN page from CentOS Other wayland-devel-1.19.0-1.el8.i686.rpm

wl_shm_buffer

Section: Wayland (3)
Updated: Tue Jun 1 2021
Index 

NAME

wl_shm_buffer 

SYNOPSIS


 

Public Member Functions


void * wl_shm_buffer_get_data (struct wl_shm_buffer *buffer)

struct wl_shm_pool * wl_shm_buffer_ref_pool (struct wl_shm_buffer *buffer)

void wl_shm_buffer_begin_access (struct wl_shm_buffer *buffer)

void wl_shm_buffer_end_access (struct wl_shm_buffer *buffer)
 

Data Fields


struct wl_resource * resource

int32_t width

int32_t height

int32_t stride

uint32_t format

int offset

struct wl_shm_pool * pool
 

Member Function Documentation

 

void wl_shm_buffer_begin_access (struct wl_shm_buffer * buffer)

Mark that the given SHM buffer is about to be accessed

Parameters:

buffer The SHM buffer

An SHM buffer is a memory-mapped file given by the client. According to POSIX, reading from a memory-mapped region that extends off the end of the file will cause a SIGBUS signal to be generated. Normally this would cause the compositor to terminate. In order to make the compositor robust against clients that change the size of the underlying file or lie about its size, you should protect access to the buffer by calling this function before reading from the memory and call wl_shm_buffer_end_access afterwards. This will install a signal handler for SIGBUS which will prevent the compositor from crashing.

After calling this function the signal handler will remain installed for the lifetime of the compositor process. Note that this function will not work properly if the compositor is also installing its own handler for SIGBUS.

If a SIGBUS signal is received for an address within the range of the SHM pool of the given buffer then the client will be sent an error event when wl_shm_buffer_end_access is called. If the signal is for an address outside that range then the signal handler will reraise the signal which would will likely cause the compositor to terminate.

It is safe to nest calls to these functions as long as the nested calls are all accessing the same buffer. The number of calls to wl_shm_buffer_end_access must match the number of calls to wl_shm_buffer_begin_access. These functions are thread-safe and it is allowed to simultaneously access different buffers or the same buffer from multiple threads.  

void wl_shm_buffer_end_access (struct wl_shm_buffer * buffer)

Ends the access to a buffer started by wl_shm_buffer_begin_access

Parameters:

buffer The SHM buffer

This should be called after wl_shm_buffer_begin_access once the buffer is no longer being accessed. If a SIGBUS signal was generated in-between these two calls then the resource for the given buffer will be sent an error.  

void * wl_shm_buffer_get_data (struct wl_shm_buffer * buffer)

Get a pointer to the memory for the SHM buffer

Parameters:

buffer The buffer object

Returns a pointer which can be used to read the data contained in the given SHM buffer.

As this buffer is memory-mapped, reading from it may generate SIGBUS signals. This can happen if the client claims that the buffer is larger than it is or if something truncates the underlying file. To prevent this signal from causing the compositor to crash you should call wl_shm_buffer_begin_access and wl_shm_buffer_end_access around code that reads from the memory.  

struct wl_shm_pool * wl_shm_buffer_ref_pool (struct wl_shm_buffer * buffer)

Get a reference to a shm_buffer's shm_pool

Parameters:

buffer The buffer object

Returns a pointer to a buffer's shm_pool and increases the shm_pool refcount.

The compositor must remember to call wl_shm_pool_unref when it no longer needs the reference to ensure proper destruction of the pool.

See also:

wl_shm_pool_unref

 

Field Documentation

 

uint32_t wl_shm_buffer::format

 

int32_t wl_shm_buffer::height

 

int wl_shm_buffer::offset

 

struct wl_shm_pool* wl_shm_buffer::pool

 

struct wl_resource* wl_shm_buffer::resource

 

int32_t wl_shm_buffer::stride

 

int32_t wl_shm_buffer::width

 

Author

Generated automatically by Doxygen for Wayland from the source code.


 

Index

NAME
SYNOPSIS
Public Member Functions
Data Fields
Member Function Documentation
void wl_shm_buffer_begin_access (struct wl_shm_buffer * buffer)
void wl_shm_buffer_end_access (struct wl_shm_buffer * buffer)
void * wl_shm_buffer_get_data (struct wl_shm_buffer * buffer)
struct wl_shm_pool * wl_shm_buffer_ref_pool (struct wl_shm_buffer * buffer)
Field Documentation
uint32_t wl_shm_buffer::format
int32_t wl_shm_buffer::height
int wl_shm_buffer::offset
struct wl_shm_pool* wl_shm_buffer::pool
struct wl_resource* wl_shm_buffer::resource
int32_t wl_shm_buffer::stride
int32_t wl_shm_buffer::width
Author

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