If a process that has mmap'd a COMEDI buffer is being run under a
debugger such as GDB, the buffer contents are inaccessible from the
debugger. Support the `access()` VM operation to allow the buffer
contents to be accessed by another process.
Signed-off-by: Ian Abbott <abbotti@xxxxxxxxx>
---
drivers/staging/comedi/comedi_buf.c | 24 ++++++++++++++++++++++++
drivers/staging/comedi/comedi_fops.c | 15 +++++++++++++++
drivers/staging/comedi/comedi_internal.h | 2 ++
3 files changed, 41 insertions(+)
diff --git a/drivers/staging/comedi/comedi_buf.c b/drivers/staging/comedi/comedi_buf.c
index 1e1df89b5018..8e9b30b26810 100644
--- a/drivers/staging/comedi/comedi_buf.c
+++ b/drivers/staging/comedi/comedi_buf.c
@@ -161,6 +161,30 @@ int comedi_buf_map_put(struct comedi_buf_map *bm)
return 1;
}
+/* helper for "access" vm operation */
+int comedi_buf_map_access(struct comedi_buf_map *bm, unsigned long offset,
+ void *buf, int len, int write)
+{
+ unsigned int pgoff = offset & ~PAGE_MASK;
+ unsigned long pg = offset >> PAGE_SHIFT;
+ int done = 0;
+
+ while (done < len && pg < bm->n_pages) {
+ int l = min_t(int, len - done, PAGE_SIZE - pgoff);
+ void *b = bm->page_list[pg].virt_addr + pgoff;
+
+ if (write)
+ memcpy(b, buf, l);
+ else
+ memcpy(buf, b, l);
+ buf += l;
+ done += l;
+ pg++;
+ pgoff = 0;
+ }
+ return done;
+}
+
/* returns s->async->buf_map and increments its kref refcount */
struct comedi_buf_map *
comedi_buf_map_from_subdev_get(struct comedi_subdevice *s)
diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index 92d864fc08ac..2a8a39653c94 100644
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -2165,9 +2165,24 @@ static void comedi_vm_close(struct vm_area_struct *area)
comedi_buf_map_put(bm);
}
+static int comedi_vm_access(struct vm_area_struct *vma, unsigned long addr,
+ void *buf, int len, int write)
+{
+ struct comedi_buf_map *bm = vma->vm_private_data;
+ unsigned long offset =
+ addr - vma->vm_start + (vma->vm_pgoff << PAGE_SHIFT);
+
+ if (len < 0)
+ return -EINVAL;
+ if (len > vma->vm_end - vma->vm_start)
+ len = vma->vm_end - vma->vm_start;
+ return comedi_buf_map_access(bm, offset, buf, len, write);
+}
+
static const struct vm_operations_struct comedi_vm_ops = {
.open = comedi_vm_open,
.close = comedi_vm_close,
+ .access = comedi_vm_access,
};
static int comedi_mmap(struct file *file, struct vm_area_struct *vma)
diff --git a/drivers/staging/comedi/comedi_internal.h b/drivers/staging/comedi/comedi_internal.h
index 534415e331b6..6246f4a78ca6 100644
--- a/drivers/staging/comedi/comedi_internal.h
+++ b/drivers/staging/comedi/comedi_internal.h
@@ -29,6 +29,8 @@ void comedi_buf_reset(struct comedi_subdevice *s);
bool comedi_buf_is_mmapped(struct comedi_subdevice *s);
void comedi_buf_map_get(struct comedi_buf_map *bm);
int comedi_buf_map_put(struct comedi_buf_map *bm);
+int comedi_buf_map_access(struct comedi_buf_map *bm, unsigned long offset,
+ void *buf, int len, int write);
struct comedi_buf_map *comedi_buf_map_from_subdev_get(
struct comedi_subdevice *s);
unsigned int comedi_buf_write_n_available(struct comedi_subdevice *s);
--
2.11.0
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