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kraxelkraxel
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Add udmabuf misc device
A driver to let userspace turn memfd regions into dma-bufs. Use case: Allows qemu create dmabufs for the vga framebuffer or virtio-gpu ressources. Then they can be passed around to display those guest things on the host. To spice client for classic full framebuffer display, and hopefully some day to wayland server for seamless guest window display. qemu test branch: https://git.kraxel.org/cgit/qemu/log/?h=sirius/udmabuf Cc: David Airlie <[email protected]> Cc: Tomeu Vizoso <[email protected]> Cc: Laurent Pinchart <[email protected]> Cc: Daniel Vetter <[email protected]> Signed-off-by: Gerd Hoffmann <[email protected]> Acked-by: Daniel Vetter <[email protected]> Link: http://patchwork.freedesktop.org/patch/msgid/[email protected]
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‎Documentation/ioctl/ioctl-number.txt‎

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@@ -272,6 +272,7 @@ Code Seq#(hex) Include File Comments
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't' 90-91 linux/toshiba.h toshiba and toshiba_acpi SMM
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'u' 00-1F linux/smb_fs.h gone
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'u' 20-3F linux/uvcvideo.h USB video class host driver
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'u' 40-4f linux/udmabuf.h userspace dma-buf misc device
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'v' 00-1F linux/ext2_fs.h conflict!
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'v' 00-1F linux/fs.h conflict!
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'v' 00-0F linux/sonypi.h conflict!

‎MAINTAINERS‎

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@@ -15343,6 +15343,14 @@ F: arch/x86/um/
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F: fs/hostfs/
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F: fs/hppfs/
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USERSPACE DMA BUFFER DRIVER
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M: Gerd Hoffmann <[email protected]>
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S: Maintained
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L: [email protected]
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F: drivers/dma-buf/udmabuf.c
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F: include/uapi/linux/udmabuf.h
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T: git git://anongit.freedesktop.org/drm/drm-misc
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USERSPACE I/O (UIO)
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M: Greg Kroah-Hartman <[email protected]>
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S: Maintained

‎drivers/dma-buf/Kconfig‎

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@@ -30,4 +30,12 @@ config SW_SYNC
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WARNING: improper use of this can result in deadlocking kernel
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drivers from userspace. Intended for test and debug only.
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config UDMABUF
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bool "userspace dmabuf misc driver"
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default n
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depends on DMA_SHARED_BUFFER
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help
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A driver to let userspace turn memfd regions into dma-bufs.
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Qemu can use this to create host dmabufs for guest framebuffers.
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endmenu

‎drivers/dma-buf/Makefile‎

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@@ -1,3 +1,4 @@
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obj-y := dma-buf.o dma-fence.o dma-fence-array.o reservation.o seqno-fence.o
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obj-$(CONFIG_SYNC_FILE) += sync_file.o
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obj-$(CONFIG_SW_SYNC) += sw_sync.o sync_debug.o
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obj-$(CONFIG_UDMABUF) += udmabuf.o

‎drivers/dma-buf/udmabuf.c‎

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// SPDX-License-Identifier: GPL-2.0
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#include <linux/init.h>
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#include <linux/module.h>
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#include <linux/device.h>
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#include <linux/kernel.h>
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#include <linux/slab.h>
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#include <linux/miscdevice.h>
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#include <linux/dma-buf.h>
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#include <linux/highmem.h>
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#include <linux/cred.h>
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#include <linux/shmem_fs.h>
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#include <linux/memfd.h>
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#include <uapi/linux/udmabuf.h>
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struct udmabuf {
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u32 pagecount;
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struct page **pages;
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};
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static int udmabuf_vm_fault(struct vm_fault *vmf)
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{
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struct vm_area_struct *vma = vmf->vma;
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struct udmabuf *ubuf = vma->vm_private_data;
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if (WARN_ON(vmf->pgoff >= ubuf->pagecount))
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return VM_FAULT_SIGBUS;
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vmf->page = ubuf->pages[vmf->pgoff];
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get_page(vmf->page);
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return 0;
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}
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static const struct vm_operations_struct udmabuf_vm_ops = {
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.fault = udmabuf_vm_fault,
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};
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static int mmap_udmabuf(struct dma_buf *buf, struct vm_area_struct *vma)
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{
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struct udmabuf *ubuf = buf->priv;
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if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0)
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return -EINVAL;
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vma->vm_ops = &udmabuf_vm_ops;
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vma->vm_private_data = ubuf;
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return 0;
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}
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static struct sg_table *map_udmabuf(struct dma_buf_attachment *at,
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enum dma_data_direction direction)
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{
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struct udmabuf *ubuf = at->dmabuf->priv;
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struct sg_table *sg;
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sg = kzalloc(sizeof(*sg), GFP_KERNEL);
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if (!sg)
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goto err1;
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if (sg_alloc_table_from_pages(sg, ubuf->pages, ubuf->pagecount,
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0, ubuf->pagecount << PAGE_SHIFT,
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GFP_KERNEL) < 0)
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goto err2;
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if (!dma_map_sg(at->dev, sg->sgl, sg->nents, direction))
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goto err3;
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return sg;
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err3:
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sg_free_table(sg);
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err2:
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kfree(sg);
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err1:
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return ERR_PTR(-ENOMEM);
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}
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static void unmap_udmabuf(struct dma_buf_attachment *at,
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struct sg_table *sg,
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enum dma_data_direction direction)
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{
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sg_free_table(sg);
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kfree(sg);
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}
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static void release_udmabuf(struct dma_buf *buf)
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{
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struct udmabuf *ubuf = buf->priv;
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pgoff_t pg;
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for (pg = 0; pg < ubuf->pagecount; pg++)
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put_page(ubuf->pages[pg]);
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kfree(ubuf->pages);
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kfree(ubuf);
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}
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static void *kmap_udmabuf(struct dma_buf *buf, unsigned long page_num)
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{
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struct udmabuf *ubuf = buf->priv;
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struct page *page = ubuf->pages[page_num];
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return kmap(page);
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}
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static void kunmap_udmabuf(struct dma_buf *buf, unsigned long page_num,
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void *vaddr)
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{
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kunmap(vaddr);
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}
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static struct dma_buf_ops udmabuf_ops = {
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.map_dma_buf = map_udmabuf,
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.unmap_dma_buf = unmap_udmabuf,
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.release = release_udmabuf,
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.map = kmap_udmabuf,
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.unmap = kunmap_udmabuf,
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.mmap = mmap_udmabuf,
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};
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#define SEALS_WANTED (F_SEAL_SHRINK)
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#define SEALS_DENIED (F_SEAL_WRITE)
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static long udmabuf_create(struct udmabuf_create_list *head,
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struct udmabuf_create_item *list)
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{
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DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
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struct file *memfd = NULL;
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struct udmabuf *ubuf;
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struct dma_buf *buf;
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pgoff_t pgoff, pgcnt, pgidx, pgbuf;
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struct page *page;
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int seals, ret = -EINVAL;
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u32 i, flags;
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ubuf = kzalloc(sizeof(struct udmabuf), GFP_KERNEL);
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if (!ubuf)
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return -ENOMEM;
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for (i = 0; i < head->count; i++) {
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if (!IS_ALIGNED(list[i].offset, PAGE_SIZE))
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goto err_free_ubuf;
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if (!IS_ALIGNED(list[i].size, PAGE_SIZE))
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goto err_free_ubuf;
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ubuf->pagecount += list[i].size >> PAGE_SHIFT;
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}
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ubuf->pages = kmalloc_array(ubuf->pagecount, sizeof(struct page *),
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GFP_KERNEL);
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if (!ubuf->pages) {
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ret = -ENOMEM;
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goto err_free_ubuf;
149+
}
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pgbuf = 0;
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for (i = 0; i < head->count; i++) {
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memfd = fget(list[i].memfd);
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if (!memfd)
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goto err_put_pages;
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if (!shmem_mapping(file_inode(memfd)->i_mapping))
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goto err_put_pages;
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seals = memfd_fcntl(memfd, F_GET_SEALS, 0);
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if (seals == -EINVAL ||
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(seals & SEALS_WANTED) != SEALS_WANTED ||
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(seals & SEALS_DENIED) != 0)
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goto err_put_pages;
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pgoff = list[i].offset >> PAGE_SHIFT;
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pgcnt = list[i].size >> PAGE_SHIFT;
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for (pgidx = 0; pgidx < pgcnt; pgidx++) {
166+
page = shmem_read_mapping_page(
167+
file_inode(memfd)->i_mapping, pgoff + pgidx);
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if (IS_ERR(page)) {
169+
ret = PTR_ERR(page);
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goto err_put_pages;
171+
}
172+
ubuf->pages[pgbuf++] = page;
173+
}
174+
fput(memfd);
175+
}
176+
memfd = NULL;
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exp_info.ops = &udmabuf_ops;
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exp_info.size = ubuf->pagecount << PAGE_SHIFT;
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exp_info.priv = ubuf;
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buf = dma_buf_export(&exp_info);
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if (IS_ERR(buf)) {
184+
ret = PTR_ERR(buf);
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goto err_put_pages;
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}
187+
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flags = 0;
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if (head->flags & UDMABUF_FLAGS_CLOEXEC)
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flags |= O_CLOEXEC;
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return dma_buf_fd(buf, flags);
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err_put_pages:
194+
while (pgbuf > 0)
195+
put_page(ubuf->pages[--pgbuf]);
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err_free_ubuf:
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fput(memfd);
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kfree(ubuf->pages);
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kfree(ubuf);
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return ret;
201+
}
202+
203+
static long udmabuf_ioctl_create(struct file *filp, unsigned long arg)
204+
{
205+
struct udmabuf_create create;
206+
struct udmabuf_create_list head;
207+
struct udmabuf_create_item list;
208+
209+
if (copy_from_user(&create, (void __user *)arg,
210+
sizeof(struct udmabuf_create)))
211+
return -EFAULT;
212+
213+
head.flags = create.flags;
214+
head.count = 1;
215+
list.memfd = create.memfd;
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list.offset = create.offset;
217+
list.size = create.size;
218+
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return udmabuf_create(&head, &list);
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}
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static long udmabuf_ioctl_create_list(struct file *filp, unsigned long arg)
223+
{
224+
struct udmabuf_create_list head;
225+
struct udmabuf_create_item *list;
226+
int ret = -EINVAL;
227+
u32 lsize;
228+
229+
if (copy_from_user(&head, (void __user *)arg, sizeof(head)))
230+
return -EFAULT;
231+
if (head.count > 1024)
232+
return -EINVAL;
233+
lsize = sizeof(struct udmabuf_create_item) * head.count;
234+
list = memdup_user((void __user *)(arg + sizeof(head)), lsize);
235+
if (IS_ERR(list))
236+
return PTR_ERR(list);
237+
238+
ret = udmabuf_create(&head, list);
239+
kfree(list);
240+
return ret;
241+
}
242+
243+
static long udmabuf_ioctl(struct file *filp, unsigned int ioctl,
244+
unsigned long arg)
245+
{
246+
long ret;
247+
248+
switch (ioctl) {
249+
case UDMABUF_CREATE:
250+
ret = udmabuf_ioctl_create(filp, arg);
251+
break;
252+
case UDMABUF_CREATE_LIST:
253+
ret = udmabuf_ioctl_create_list(filp, arg);
254+
break;
255+
default:
256+
ret = -EINVAL;
257+
break;
258+
}
259+
return ret;
260+
}
261+
262+
static const struct file_operations udmabuf_fops = {
263+
.owner = THIS_MODULE,
264+
.unlocked_ioctl = udmabuf_ioctl,
265+
};
266+
267+
static struct miscdevice udmabuf_misc = {
268+
.minor = MISC_DYNAMIC_MINOR,
269+
.name = "udmabuf",
270+
.fops = &udmabuf_fops,
271+
};
272+
273+
static int __init udmabuf_dev_init(void)
274+
{
275+
return misc_register(&udmabuf_misc);
276+
}
277+
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static void __exit udmabuf_dev_exit(void)
279+
{
280+
misc_deregister(&udmabuf_misc);
281+
}
282+
283+
module_init(udmabuf_dev_init)
284+
module_exit(udmabuf_dev_exit)
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MODULE_AUTHOR("Gerd Hoffmann <[email protected]>");
287+
MODULE_LICENSE("GPL v2");

‎include/uapi/linux/udmabuf.h‎

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/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
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#ifndef _UAPI_LINUX_UDMABUF_H
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#define _UAPI_LINUX_UDMABUF_H
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#include <linux/types.h>
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#include <linux/ioctl.h>
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8+
#define UDMABUF_FLAGS_CLOEXEC 0x01
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struct udmabuf_create {
11+
__u32 memfd;
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__u32 flags;
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__u64 offset;
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__u64 size;
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};
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struct udmabuf_create_item {
18+
__u32 memfd;
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__u32 __pad;
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__u64 offset;
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__u64 size;
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};
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struct udmabuf_create_list {
25+
__u32 flags;
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__u32 count;
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struct udmabuf_create_item list[];
28+
};
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#define UDMABUF_CREATE _IOW('u', 0x42, struct udmabuf_create)
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#define UDMABUF_CREATE_LIST _IOW('u', 0x43, struct udmabuf_create_list)
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#endif /* _UAPI_LINUX_UDMABUF_H */

‎tools/testing/selftests/drivers/dma-buf/Makefile‎

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CFLAGS += -I../../../../../usr/include/
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TEST_GEN_PROGS := udmabuf
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include ../../lib.mk

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