gstreamer/subprojects/gst-plugins-base/gst-libs/gst/allocators/gstshmallocator.c

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/* GStreamer shared memory allocator
*
* Copyright (C) 2012 Intel Corporation
* Copyright (C) 2012 Sreerenj Balachandran <sreerenj.balachandran@intel.com>
* Copyright (C) 2023 Netflix Inc.
* Author: Xavier Claessens <xavier.claessens@collabora.com>
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public
* License along with this library; if not, write to the
* Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
* Boston, MA 02110-1301, USA.
*/
/**
* SECTION:gstshmallocator
* @title: GstShmAllocator
* @short_description: Allocator for file-descriptor backed shared memory
* @see_also: #GstMemory and #GstFdAllocator
*
* This is a subclass of #GstFdAllocator that implements the
* gst_allocator_alloc() method using `memfd_create()` when available, POSIX
* `shm_open()` otherwise. Platforms not supporting any of those (Windows) will
* always return %NULL.
*
* Note that allocating new shared memories has a significant performance cost,
* it is thus recommended to keep a pool of pre-allocated #GstMemory, using
* #GstBufferPool. For that reason, this allocator has the
* %GST_ALLOCATOR_FLAG_NO_COPY flag set.
*
* Since: 1.24
*/
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <sys/stat.h>
#include "gstshmallocator.h"
#ifdef HAVE_MMAP
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/mman.h>
#endif
struct _GstShmAllocator
{
GstFdAllocator parent;
};
#define GST_CAT_DEFAULT gst_shm_debug
GST_DEBUG_CATEGORY_STATIC (GST_CAT_DEFAULT);
G_DEFINE_TYPE_WITH_CODE (GstShmAllocator, gst_shm_allocator,
GST_TYPE_FD_ALLOCATOR,
GST_DEBUG_CATEGORY_INIT (gst_shm_debug, "shmallocator", 0,
"Shared memory allocator");
);
static GstMemory *
gst_shm_allocator_alloc (GstAllocator * allocator, gsize size,
GstAllocationParams * params)
{
#if defined(HAVE_MEMFD_CREATE) || defined(HAVE_SHM_OPEN)
GstShmAllocator *self = GST_SHM_ALLOCATOR (allocator);
int fd;
GstMemory *mem;
GstMapInfo info;
/* See _sysmem_new_block() for details */
gsize maxsize = size + params->prefix + params->padding;
gsize align = params->align;
align |= gst_memory_alignment;
maxsize += align;
#ifdef HAVE_MEMFD_CREATE
fd = memfd_create ("gst-shm", MFD_CLOEXEC | MFD_ALLOW_SEALING);
if (fd < 0) {
GST_ERROR_OBJECT (self, "memfd_create() failed: %s", strerror (errno));
return NULL;
}
#else
{
char filename[1024];
static int init = 0;
int flags = O_RDWR | O_CREAT | O_EXCL;
int perms = S_IRUSR | S_IWUSR | S_IRGRP;
snprintf (filename, 1024, "/gst-shm.%d.%d", getpid (), init++);
fd = shm_open (filename, flags, perms);
if (fd < 0) {
GST_ERROR_OBJECT (self, "shm_open() failed: %s", strerror (errno));
return NULL;
}
shm_unlink (filename);
}
#endif
if (ftruncate (fd, maxsize) < 0) {
GST_ERROR_OBJECT (self, "ftruncate failed: %s", strerror (errno));
close (fd);
return NULL;
}
mem = gst_fd_allocator_alloc (allocator, fd, maxsize,
GST_FD_MEMORY_FLAG_KEEP_MAPPED);
if (G_UNLIKELY (!mem)) {
GST_ERROR_OBJECT (self, "GstFdMemory allocation failed");
close (fd);
return NULL;
}
/* We use GST_FD_MEMORY_FLAG_KEEP_MAPPED, so make sure the first map is RW. */
if (!gst_memory_map (mem, &info, GST_MAP_READWRITE)) {
GST_ERROR_OBJECT (self, "GstFdMemory map failed");
gst_memory_unref (mem);
return NULL;
}
/* See _sysmem_new_block() for details */
guint8 *data = info.data;
gsize aoffset;
gsize asize = maxsize;
if ((aoffset = ((guintptr) data & align))) {
aoffset = (align + 1) - aoffset;
data += aoffset;
asize = maxsize - aoffset;
}
if (params->prefix && (params->flags & GST_MEMORY_FLAG_ZERO_PREFIXED))
memset (data, 0, params->prefix);
gsize padding = asize - (params->prefix + size);
if (padding && (params->flags & GST_MEMORY_FLAG_ZERO_PADDED))
memset (data + params->prefix + size, 0, padding);
mem->align = align;
mem->size = size;
mem->offset = params->prefix + aoffset;
gst_memory_unmap (mem, &info);
#ifdef HAVE_MEMFD_CREATE
fcntl (fd, F_ADD_SEALS, F_SEAL_SHRINK);
#endif
return mem;
#else
return NULL;
#endif
}
static void
gst_shm_allocator_class_init (GstShmAllocatorClass * klass)
{
GstAllocatorClass *alloc_class = (GstAllocatorClass *) klass;
alloc_class->alloc = GST_DEBUG_FUNCPTR (gst_shm_allocator_alloc);
}
static void
gst_shm_allocator_init (GstShmAllocator * self)
{
GstAllocator *alloc = GST_ALLOCATOR_CAST (self);
alloc->mem_type = GST_ALLOCATOR_SHM;
GST_OBJECT_FLAG_SET (self, GST_ALLOCATOR_FLAG_NO_COPY);
}
/**
* gst_shm_allocator_init_once:
*
* Register a #GstShmAllocator using gst_allocator_register() with the name
* %GST_ALLOCATOR_SHM. This is no-op after the first call.
*
* Since: 1.24
*/
void
gst_shm_allocator_init_once (void)
{
static gsize _init = 0;
if (g_once_init_enter (&_init)) {
GstAllocator *alloc;
alloc = (GstAllocator *) g_object_new (GST_TYPE_SHM_ALLOCATOR, NULL);
gst_object_ref_sink (alloc);
gst_allocator_register (GST_ALLOCATOR_SHM, alloc);
g_once_init_leave (&_init, 1);
}
}
/**
* gst_shm_allocator_get:
*
* Get the #GstShmAllocator singleton previously registered with
* gst_shm_allocator_init_once().
*
* Returns: (transfer full) (nullable): a #GstAllocator or %NULL if
* gst_shm_allocator_init_once() has not been previously called.
*
* Since: 1.24
*/
GstAllocator *
gst_shm_allocator_get (void)
{
return gst_allocator_find (GST_ALLOCATOR_SHM);
}