Re: [RFC simple allocator v2 1/2] Create Simple Allocator module

2017-02-14 20:30 GMT+01:00 Laurent Pinchart [off-list ref]:

Hi Benjamin,

Thank you for the patch. I've CC'ed the linux-api mailing list.

On Monday 13 Feb 2017 15:45:05 Benjamin Gaignard wrote:

quoted

This is the core of simple allocator module.
It aim to offert one common ioctl to allocate specific memory.

version 2:
- rebased on 4.10-rc7

Signed-off-by: Benjamin Gaignard <redacted>
---
 Documentation/simple-allocator.txt              |  81 +++++++++++
 drivers/Kconfig                                 |   2 +
 drivers/Makefile                                |   1 +
 drivers/simpleallocator/Kconfig                 |  10 ++
 drivers/simpleallocator/Makefile                |   1 +
 drivers/simpleallocator/simple-allocator-priv.h |  33 +++++
 drivers/simpleallocator/simple-allocator.c      | 180 +++++++++++++++++++++
 include/uapi/linux/simple-allocator.h           |  35 +++++
 8 files changed, 343 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-priv.h
 create mode 100644 drivers/simpleallocator/simple-allocator.c
 create mode 100644 include/uapi/linux/simple-allocator.h

diff --git a/Documentation/simple-allocator.txt

b/Documentation/simple-allocator.txt new file mode 100644
index 0000000..89ba883

--- /dev/null
+++ b/Documentation/simple-allocator.txt

@@ -0,0 +1,81 @@
+Simple Allocator Framework

There's nothing simple in buffer allocation, otherwise we would have solved
the problem a long time ago. Let's not use a misleading name.

Simple was not about the problem, it was about the using only one ioctl.
Anyway a better name is needed: "Limited allocation API", "Basic
allocator framework" ?
suggestions are welcomes

quoted

+Simple Allocator offer a single ioctl SA_IOC_ALLOC to allocate buffers
+on dedicated memory regions and export them as a dmabuf file descriptor.
+Using dmabuf file descriptor allow to share this memory between processes
+and/or import it into other frameworks like v4l2 or drm/kms (prime).
+When userland wants to free the memory only a call to close() in needed
+so it could done even without knowing that buffer has been allocated by
+simple allocator ioctl.
+
+Each memory regions will be seen as a filein /dev/.
+For example CMA regions will exposed has /dev/cmaX.

Why do you need multiple devices ? Furthermore, given how central this API
will become, I believe it needs very strict review, and would be a candidate
for a syscall.

I believe that having a device per memory regions is simple than have having,
like ION, heaps which request to add masks (or heap ids) to select them.
My goal here is not to have a a central device /dev/simple_allocator
where allcoations
are dispatched over heaps but only a common ioctl to make userland life easier.
Maybe I should regroup all the device under the same directory: /dev/simple/ ?

Without diving into details yet, there are a few particular points I'm
concerned about.

- What is the scope of this API ? What problems do you want to solve, plan to
solve in the future, and consider as out of scope ?

My problem is to be able to allocate a buffer in contiguous memory
(CMA) when using
a software decoder and Weston. This will save the copy between decoder
and display
because display only accepted contiguous memory.
Wayland dmabuf protocol can't allocate buffers so I need an other way
to get access to CMA.
I also other use cases where I need to allocate memory in special
memory region for secure
purpose.

For those both cases I need an API to allocate memory from userland so
I decided to
propose a common ioctl which may be used for even more memory regions.

- How should we handle permissions and resource limits ? Is file-based
permission on a device node a good model ? How do we prevent or at least
mitigate memory-related DoS ?

Since each memory region will be represented by a device we could set per
device permissions for example with SELinux policy.

- How should such a central allocator API interact with containers and
virtualization in general ?

I'm not expert enough in container and virtualization but I know they could have
access to some files/directories to store data so I guess it will
possible for them
to call (for example) /dev/cma0  to allocate memory

- What model do we want to expose to applications to select a memory type ?
You still haven't convinced me that we should expose memory pools explicitly
to application (à la ION), and I believe a usage/constraint model would be
better.

Memory type selection should be solved by something more smarter than my code.
My goal here is only to provided a common way to perform allocations.
If  "Unix Device Memory Allocator" project manage to define a way to expose
memory constraint I plan to add one ioctl to let it know the
capabilities of each memory region.
I hope that what I'm proposing could become a backend for "Unix Device
Memory Allocator".

quoted

+Implementing a simple allocator
+-------------------------------
+
+Simple Allocator provide helpers functions to register/unregister an
+allocator:
+- simple_allocator_register(struct sa_device *sadev)
+  Register simple_allocator_device using sa_device structure where name,
+  owner and allocate fields must be set.
+
+- simple_allocator_unregister(struct sa_device *sadev)
+  Unregister a simple allocator device.
+
+Using Simple Allocator /dev interface example
+---------------------------------------------
+
+This example of code allocate a buffer on the first CMA region (/dev/cma0)
+before mmap and close it.
+
+#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);
+}

diff --git a/drivers/Kconfig b/drivers/Kconfig
index e1e2066..a6d8828 100644
--- a/drivers/Kconfig
+++ b/drivers/Kconfig

@@ -202,4 +202,6 @@ source "drivers/hwtracing/intel_th/Kconfig"

 source "drivers/fpga/Kconfig"

+source "drivers/simpleallocator/Kconfig"
+
 endmenu

diff --git a/drivers/Makefile b/drivers/Makefile
index 060026a..5081eb8 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile

@@ -173,3 +173,4 @@ obj-$(CONFIG_STM)         += hwtracing/stm/
 obj-$(CONFIG_ANDROID)                += android/
 obj-$(CONFIG_NVMEM)          += nvmem/
 obj-$(CONFIG_FPGA)           += fpga/
+obj-$(CONFIG_SIMPLE_ALLOCATOR)       += simpleallocator/

diff --git a/drivers/simpleallocator/Kconfig

b/drivers/simpleallocator/Kconfig new file mode 100644
index 0000000..c6fc2e3

--- /dev/null
+++ b/drivers/simpleallocator/Kconfig

@@ -0,0 +1,10 @@
+menu "Simple Allocator"
+
+config SIMPLE_ALLOCATOR
+     tristate "Simple Alllocator Framework"
+     select DMA_SHARED_BUFFER
+     ---help---
+        The Simple Allocator Framework adds an API to allocate and share
+        memory in userland.
+
+endmenu

diff --git a/drivers/simpleallocator/Makefile

b/drivers/simpleallocator/Makefile new file mode 100644
index 0000000..e27c6ad

--- /dev/null
+++ b/drivers/simpleallocator/Makefile

@@ -0,0 +1 @@
+obj-$(CONFIG_SIMPLE_ALLOCATOR) += simple-allocator.o

diff --git a/drivers/simpleallocator/simple-allocator-priv.h

b/drivers/simpleallocator/simple-allocator-priv.h new file mode 100644
index 0000000..33f5a33

--- /dev/null
+++ b/drivers/simpleallocator/simple-allocator-priv.h

@@ -0,0 +1,33 @@
+/*
+ * Copyright (C) Linaro 2016
+ *
+ * Author: Benjamin Gaignard <benjamin.gaignard-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
+ *
+ * License terms:  GNU General Public License (GPL)
+ */
+
+#ifndef _SIMPLE_ALLOCATOR_PRIV_H_
+#define _SIMPLE_ALLOCATOR_PRIV_H_
+
+#include <linux/cdev.h>
+#include <linux/device.h>
+#include <linux/dma-buf.h>
+
+/**
+ * struct sa_device - simple allocator device
+ * @owner: module owner, must be set to THIS_MODULE
+ * @name: name of the allocator
+ * @allocate: callabck for memory allocation
+ */
+struct sa_device {
+     struct device   dev;
+     struct cdev     chrdev;
+     struct module   *owner;
+     const char      *name;
+     struct dma_buf *(*allocate)(struct sa_device *, u64 length, u32

flags);

quoted

+};
+
+int simple_allocator_register(struct sa_device *sadev);
+void simple_allocator_unregister(struct sa_device *sadev);
+
+#endif

diff --git a/drivers/simpleallocator/simple-allocator.c

b/drivers/simpleallocator/simple-allocator.c new file mode 100644
index 0000000..d89ccbf

--- /dev/null
+++ b/drivers/simpleallocator/simple-allocator.c

@@ -0,0 +1,180 @@
+/*
+ * Copyright (C) Linaro 2016
+ *
+ * Author: Benjamin Gaignard <benjamin.gaignard-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
+ *
+ * License terms:  GNU General Public License (GPL)
+ */
+
+#include <linux/module.h>
+#include <linux/simple-allocator.h>
+#include <linux/uaccess.h>
+
+#include "simple-allocator-priv.h"
+
+#define SA_MAJOR     222
+#define SA_NUM_DEVICES       256
+#define SA_NAME              "simple_allocator"
+
+static int sa_minor;
+
+static struct class sa_class = {
+     .name = SA_NAME,
+};
+
+static long sa_ioctl(struct file *filp, unsigned int cmd, unsigned long

arg) +{
+     struct sa_device *sadev = filp->private_data;
+     int ret = -ENODEV;
+
+     switch (cmd) {
+     case SA_IOC_ALLOC:
+     {
+             struct simple_allocate_data data;
+             struct dma_buf *dmabuf;
+
+             if (copy_from_user(&data, (void __user *)arg, _IOC_SIZE(cmd)))
+                     return -EFAULT;
+
+             if (data.version != 0)
+                     return -EINVAL;
+
+             dmabuf = sadev->allocate(sadev, data.length, data.flags);
+             if (!dmabuf)
+                     return -EINVAL;
+
+             data.fd = dma_buf_fd(dmabuf, data.flags);
+             if (data.fd < 0) {
+                     dma_buf_put(dmabuf);
+                     return -EINVAL;
+             }
+
+             data.length = dmabuf->size;
+
+             if (copy_to_user((void __user *)arg, &data, _IOC_SIZE(cmd))) {
+                     dma_buf_put(dmabuf);
+                     return -EFAULT;
+             }
+
+             return 0;
+     }
+     }
+     return ret;
+}
+
+static int sa_open(struct inode *inode, struct file *filp)
+{
+     struct sa_device *sadev = container_of(inode->i_cdev,
+                                            struct sa_device, chrdev);
+
+     if (!sadev)
+             return -ENODEV;
+
+     get_device(&sadev->dev);
+     filp->private_data = sadev;
+     return 0;
+}
+
+static int sa_release(struct inode *inode, struct file *filp)
+{
+     struct sa_device *sadev = container_of(inode->i_cdev,
+                                            struct sa_device, chrdev);
+
+     if (!sadev)
+             return -ENODEV;
+
+     put_device(&sadev->dev);
+     return 0;
+}
+
+static const struct file_operations sa_fops = {
+     .owner = THIS_MODULE,
+     .open = sa_open,
+     .release = sa_release,
+     .unlocked_ioctl = sa_ioctl,
+};
+
+/**
+ * simple_allocator_register - register a simple allocator
+ * @sadev: simple allocator structure to be registered
+ *
+ * Return 0 if allocator has been regsitered, either a negative value.
+ */
+int simple_allocator_register(struct sa_device *sadev)
+{
+     int ret;
+
+     if (!sadev->name || !sadev->allocate)
+             return -EINVAL;
+
+     cdev_init(&sadev->chrdev, &sa_fops);
+     sadev->chrdev.owner = sadev->owner;
+
+     ret = cdev_add(&sadev->chrdev, MKDEV(SA_MAJOR, sa_minor), 1);
+     if (ret < 0)
+             return ret;
+
+     sadev->dev.class = &sa_class;
+     sadev->dev.devt = MKDEV(SA_MAJOR, sa_minor);
+     dev_set_name(&sadev->dev, "%s%d", sadev->name, sa_minor);
+     ret = device_register(&sadev->dev);
+     if (ret < 0)
+             goto cleanup;
+
+     sa_minor++;
+     return 0;
+
+cleanup:
+     cdev_del(&sadev->chrdev);
+     return ret;
+}
+EXPORT_SYMBOL_GPL(simple_allocator_register);
+
+/**
+ * simple_allocator_unregister - unregister a simple allocator
+ * @sadev: simple allocator device to be unregistered
+ */
+void simple_allocator_unregister(struct sa_device *sadev)
+{
+     if (!sadev)
+             return;
+
+     cdev_del(&sadev->chrdev);
+     device_del(&sadev->dev);
+     put_device(&sadev->dev);
+}
+EXPORT_SYMBOL_GPL(simple_allocator_unregister);
+
+static int __init sa_init(void)
+{
+     dev_t dev = MKDEV(SA_MAJOR, 0);
+     int ret;
+
+     ret = register_chrdev_region(dev, SA_NUM_DEVICES, SA_NAME);
+     if (ret < 0)
+             return ret;
+
+     ret = class_register(&sa_class);
+     if (ret < 0) {
+             unregister_chrdev_region(dev, SA_NUM_DEVICES);
+             return -EIO;
+     }
+
+     return 0;
+}
+
+static void __exit sa_exit(void)
+{
+     dev_t dev = MKDEV(SA_MAJOR, 0);
+
+     class_unregister(&sa_class);
+     unregister_chrdev_region(dev, SA_NUM_DEVICES);
+}
+
+subsys_initcall(sa_init);
+module_exit(sa_exit);
+
+MODULE_AUTHOR("Benjamin Gaignard [off-list ref]");
+MODULE_DESCRIPTION("Simple allocator");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS_CHARDEV_MAJOR(SA_MAJOR);

diff --git a/include/uapi/linux/simple-allocator.h

b/include/uapi/linux/simple-allocator.h new file mode 100644
index 0000000..5520a85

--- /dev/null
+++ b/include/uapi/linux/simple-allocator.h

@@ -0,0 +1,35 @@
+/*
+ * Copyright (C) Linaro 2016
+ *
+ * Author: Benjamin Gaignard <benjamin.gaignard-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
+ *
+ * License terms:  GNU General Public License (GPL), version 2
+ */
+
+#ifndef _SIMPLE_ALLOCATOR_H_
+#define _SIMPLE_ALLOCATOR_H_
+
+#include <linux/ioctl.h>
+#include <linux/types.h>
+
+/**
+ * struct simple_allocate_data - allocation parameters
+ * @version: structure version (must be set to 0)
+ * @length:  size of the requested buffer
+ * @flags:   mode flags for the file like O_RDWR or O_CLOEXEC
+ * @fd:              returned file descriptor
+ */
+struct simple_allocate_data {
+     __u64 version;
+     __u64 length;
+     __u32 flags;
+     __u32 reserved1;
+     __s32 fd;
+     __u32 reserved2;
+};
+
+#define SA_IOC_MAGIC 'S'
+
+#define SA_IOC_ALLOC _IOWR(SA_IOC_MAGIC, 0, struct simple_allocate_data)
+
+#endif

--
Regards,

Laurent Pinchart

-- 
Benjamin Gaignard

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