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staging: comedi: support vm_access_process for mmap'd buffer

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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@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ian Abbott 2017-04-20 19:05:14 +01:00 committed by Greg Kroah-Hartman
parent e44adf05b8
commit 255364f7b8
3 changed files with 41 additions and 0 deletions
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24
drivers/staging/comedi/comedi_buf.c
View File

@ -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)

15
drivers/staging/comedi/comedi_fops.c
View File

@ -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 - addr)
len = vma->vm_end - addr;
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)

2
drivers/staging/comedi/comedi_internal.h
View File

@ -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);