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

[Daniel Vetter]

On Tue, Feb 14, 2017 at 8:39 PM, Laurent Pinchart
<laurent.pinchart@xxxxxxxxxxxxxxxx> wrote:
> Hi Daniel,
>
> On Tuesday 14 Feb 2017 20:33:58 Daniel Vetter wrote:
>> On Mon, Feb 13, 2017 at 3:45 PM, Benjamin Gaignard wrote:
>> > 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 <benjamin.gaignard@xxxxxxxxxx>
>>
>> Why not ION? It's a bit a broken record question, but if there is a
>> clear answer it should be in the patch&docs ...
>
> There's a bit of love & hate relationship between Linux developers and ION.
> The API has shortcomings, and attempts to fix the issues went nowhere. As
> Laura explained, starting from a blank slate (obviously keeping in mind the
> lessons learnt so far with ION and other similar APIs) and then adding a
> wrapper to expose ION on Android systems (at least as an interim measure) was
> thought to be a better option. I still believe it is, but we seem to lack
> traction. The problem has been around for so long that I feel everybody has
> lost hope.
>
> I don't think this is unsolvable, but we need to regain motivation. In my
> opinion the first step would be to define the precise extent of the problem we
> want to solve.

I'm not sure anyone really tried hard enough (in the same way no one
tried hard enough to destage android syncpts, until last year). And
anything new should at least very clearly explain why ION (even with
the various todo items we collected at a few conferences) won't work,
and how exactly the new allocator is different from ION. I don't think
we need a full design doc (like you say, buffer allocation is hard,
we'll get it wrong anyway), but at least a proper comparison with the
existing thing. Plus explanation why we can't reuse the uabi.

Because ime when you rewrite something, you generally get one thing
right (the one thing that pissed you off about the old solution), plus
lots and lots of things that the old solution got right, wrong
(because it's all lost in the history). ADF was probably the best
example in this. KMS also took a while until all the fbdev wheels have
been properly reinvented (some are still the same old squeaky onces as
fbdev had, e.g. fbcon).

And I don't think destaging ION is going to be hard, just a bit of
work (could be a nice gsoc or whatever).
-Daniel

>
>> > ---
>> >
>> >  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
>> > +
>> > +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.
>> > +
>> > +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@xxxxxxxxxx>
>> > + *
>> > + * 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); +};
>> > +
>> > +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@xxxxxxxxxx>
>> > + *
>> > + * 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 <benjamin.gaignard@xxxxxxxxxx>");
>> > +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@xxxxxxxxxx>
>> > + *
>> > + * 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
>> > --
>> > 1.9.1
>
> --
> Regards,
>
> Laurent Pinchart
>



-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch