oracular (3) wl_shm_buffer.3.gz

NAME

       wl_shm_buffer - A 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

Detailed Description

       A SHM buffer.

       wl_shm_buffer provides a helper for accessing the contents of a wl_buffer resource created via the wl_shm
       interface.

       A wl_shm_buffer becomes invalid as soon as its wl_resource is destroyed.

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

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