It is expected that processes will pass dma-buf fd between drivers, and
only using the fd themselves for mmaping and synchronisation ioctls.
However, it may be convenient for an application to read/write into the
dma-buf, for instance a test case to check the internal
dma_buf->ops->kmap interface. There may also be a small advantage to
avoiding the mmap() for very simple/small operations.
Note in particular, synchronisation with the device is left to the
caller with an explicit DMA_BUF_IOCTL_SYNC, rather than done implicitly
inside the read/write, so that the user can avoid synchronisation if
they so choose.
"It is easier to add synchronisation later, than it is to take it away."
v2: Lots of little fixes, plus a real llseek() implements so that the
first basic little test cases work!
Testcase: igt/prime_rw
Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
Cc: Laura Abbott <labb...@redhat.com>
Cc: Sumit Semwal <sumit.sem...@linaro.org>
Cc: Daniel Vetter <daniel.vet...@ffwll.ch>
Cc: Sean Paul <seanp...@chromium.org>
Cc: Janusz Krzysztofik <janusz.krzyszto...@linux.intel.com>
Tested-by: Laura Abbott <labb...@redhat.com>
---
Dusting this off again as it would be nice as a user to operate on dmabuf
agnostic to the underyling driver. We have mmap, so naturally we would
like to have read/write as well!
---
drivers/dma-buf/dma-buf.c | 108 ++++++++++++++++++++++++++++++++------
1 file changed, 93 insertions(+), 15 deletions(-)
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 433d91d710e4..a19fc881a99c 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -135,28 +135,104 @@ static int dma_buf_mmap_internal(struct file *file,
struct vm_area_struct *vma)
static loff_t dma_buf_llseek(struct file *file, loff_t offset, int whence)
{
- struct dma_buf *dmabuf;
- loff_t base;
+ struct dma_buf *dmabuf = file->private_data;
if (!is_dma_buf_file(file))
return -EBADF;
- dmabuf = file->private_data;
+ return fixed_size_llseek(file, offset, whence, dmabuf->size);
+}
- /* only support discovering the end of the buffer,
- but also allow SEEK_SET to maintain the idiomatic
- SEEK_END(0), SEEK_CUR(0) pattern */
- if (whence == SEEK_END)
- base = dmabuf->size;
- else if (whence == SEEK_SET)
- base = 0;
- else
- return -EINVAL;
+static ssize_t dma_buf_read(struct file *file,
+ char __user *ubuf, size_t remain,
+ loff_t *offset)
+{
+ struct dma_buf *dmabuf = file->private_data;
+ unsigned long idx;
+ unsigned int start;
+ size_t total;
- if (offset != 0)
- return -EINVAL;
+ if (!is_dma_buf_file(file))
+ return -EBADF;
+
+ total = 0;
+ idx = *offset >> PAGE_SHIFT;
+ start = offset_in_page(*offset);
+ while (remain) {
+ unsigned int len = min_t(size_t, remain, PAGE_SIZE - start);
+ unsigned int copied;
+ void *vaddr;
+
+ if (*offset >= dmabuf->size)
+ return total;
+
+ vaddr = dma_buf_kmap(dmabuf, idx);
+ if (!vaddr)
+ return total ?: -EIO;
+
+ copied = copy_to_user(ubuf, vaddr + start, len);
+ dma_buf_kunmap(dmabuf, idx, vaddr);
+
+ total += copied ?: len;
+ if (copied) {
+ *offset += copied;
+ return total ?: -EFAULT;
+ }
+
+ remain -= len;
+ *offset += len;
+ ubuf += len;
+ start = 0;
+ idx++;
+ }
+
+ return total;
+}
+
+static ssize_t dma_buf_write(struct file *file,
+ const char __user *ubuf, size_t remain,
+ loff_t *offset)
+{
+ struct dma_buf *dmabuf = file->private_data;
+ unsigned long idx;
+ unsigned int start;
+ size_t total;
+
+ if (!is_dma_buf_file(file))
+ return -EBADF;
+
+ total = 0;
+ idx = *offset >> PAGE_SHIFT;
+ start = offset_in_page(*offset);
+ while (remain) {
+ unsigned int len = min_t(size_t, remain, PAGE_SIZE - start);
+ unsigned int copied;
+ void *vaddr;
+
+ if (*offset >= dmabuf->size)
+ return total;
+
+ vaddr = dma_buf_kmap(dmabuf, idx);
+ if (!vaddr)
+ return total ?: -EIO;
+
+ copied = copy_from_user(vaddr + start, ubuf, len);
+ dma_buf_kunmap(dmabuf, idx, vaddr);
+
+ total += copied ?: len;
+ if (copied) {
+ *offset += copied;
+ return total ?: -EFAULT;
+ }
+
+ remain -= len;
+ *offset += len;
+ ubuf += len;
+ start = 0;
+ idx++;
+ }
- return base + offset;
+ return total;
}
/**
@@ -413,6 +489,8 @@ static const struct file_operations dma_buf_fops = {
.release = dma_buf_release,
.mmap = dma_buf_mmap_internal,
.llseek = dma_buf_llseek,
+ .read = dma_buf_read,
+ .write = dma_buf_write,
.poll = dma_buf_poll,
.unlocked_ioctl = dma_buf_ioctl,
#ifdef CONFIG_COMPAT
--
2.23.0
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