The goal of this RFC is to understand if a common ioctl for specific memory regions allocations is needed/welcome.
Obviously it will not replace allocation done in linux kernel frameworks like v4l2, drm/kms or others, but offer an alternative when you don't want/need to use them for buffer allocation. To keep a compatibility with what already exist allocated buffers are exported in userland as dmabuf file descriptor (like ION is doing).
"Unix Device Memory Allocator" project [1] wants to create a userland library which may allow to select, depending of the devices constraint, the best back-end for allocation. With this RFC I would to propose to have common ioctl for a maximum of allocators to avoid to duplicated back-ends for this library.
One of the issues that lead me to propose this RFC it is that since the beginning it is a problem to allocate contiguous memory (CMA) without using v4l2 or drm/kms so the first allocator available in this RFC use CMA memory.
An other question is: do we have others memory regions that could be interested by this new framework ? I have in mind that some title memory regions could use it or replace ION heaps (system, carveout, etc...). Maybe it only solve CMA allocation issue, in this case there is no need to create a new framework but only a dedicated ioctl.
Maybe the first thing to do is to change the name and the location of this module, suggestions are welcome.
I have testing this code with the following program:
#include <errno.h> #include <fcntl.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <sys/ioctl.h> #include <sys/mman.h> #include <sys/stat.h> #include <sys/types.h>
#include "simple-allocator.h"
#define LENGTH 1024*16
void main (void) { struct simple_allocate_data data; int fd = open("/dev/cma0", O_RDWR, 0); int ret; void *mem;
if (fd < 0) { printf("Can't open /dev/cma0\n"); return; }
memset(&data, 0, sizeof(data));
data.length = LENGTH; data.flags = O_RDWR | O_CLOEXEC;
ret = ioctl(fd, SA_IOC_ALLOC, &data); if (ret) { printf("Buffer allocation failed\n"); goto end; }
mem = mmap(0, LENGTH, PROT_READ | PROT_WRITE, MAP_SHARED, data.fd, 0); if (mem == MAP_FAILED) { printf("mmap failed\n"); }
memset(mem, 0xFF, LENGTH); munmap(mem, LENGTH);
printf("test simple allocator CMA OK\n"); end: close(fd); }
[1] https://github.com/cubanismo/allocator
Benjamin Gaignard (2): Create Simple Allocator module add CMA simple allocator module
Documentation/simple-allocator.txt | 81 ++++++++++ drivers/Kconfig | 2 + drivers/Makefile | 1 + drivers/simpleallocator/Kconfig | 17 +++ drivers/simpleallocator/Makefile | 2 + drivers/simpleallocator/simple-allocator-cma.c | 187 ++++++++++++++++++++++++ drivers/simpleallocator/simple-allocator-priv.h | 33 +++++ drivers/simpleallocator/simple-allocator.c | 180 +++++++++++++++++++++++ include/uapi/linux/simple-allocator.h | 35 +++++ 9 files changed, 538 insertions(+) create mode 100644 Documentation/simple-allocator.txt create mode 100644 drivers/simpleallocator/Kconfig create mode 100644 drivers/simpleallocator/Makefile create mode 100644 drivers/simpleallocator/simple-allocator-cma.c create mode 100644 drivers/simpleallocator/simple-allocator-priv.h create mode 100644 drivers/simpleallocator/simple-allocator.c create mode 100644 include/uapi/linux/simple-allocator.h