Low-level comedi drivers that use the "kcomedilib" module (currently only
the "comedi_bond" driver) call `comedi_open()` to "open" another comedi
device (not as a file) and `comedi_close()` to "close" it. (Note: these
are the functions exported by the "kcomedilib" module, not the
identically named, statically linked functions in the core "comedi"
module.)
In `comedi_open()`, call `comedi_dev_get_from_minor()` instead of
`comedi_dev_from_minor()` to get the pointer to the `struct
comedi_device` being "opened". This increments its reference count to
prevent it being freed. Call `comedi_dev_put()` if `comedi_open()`
returns `NULL`, and also call it from `comedi_close()`. This decrements
the reference count.
Note that although we now protect against the `struct comedi_device`
being freed, we do not yet protect against it being "detached" while it
is being used. This will be addressed by a later patch.
Signed-off-by: Ian Abbott <abbotti@xxxxxxxxx>
---
drivers/staging/comedi/kcomedilib/kcomedilib_main.c | 19 ++++++++++++-------
1 file changed, 12 insertions(+), 7 deletions(-)
diff --git a/drivers/staging/comedi/kcomedilib/kcomedilib_main.c b/drivers/staging/comedi/kcomedilib/kcomedilib_main.c
index cd60677..b3a06f2 100644
--- a/drivers/staging/comedi/kcomedilib/kcomedilib_main.c
+++ b/drivers/staging/comedi/kcomedilib/kcomedilib_main.c
@@ -35,7 +35,7 @@ MODULE_LICENSE("GPL");
struct comedi_device *comedi_open(const char *filename)
{
- struct comedi_device *dev;
+ struct comedi_device *dev, *retval = NULL;
unsigned int minor;
if (strncmp(filename, "/dev/comedi", 11) != 0)
@@ -46,15 +46,19 @@ struct comedi_device *comedi_open(const char *filename)
if (minor >= COMEDI_NUM_BOARD_MINORS)
return NULL;
- dev = comedi_dev_from_minor(minor);
-
- if (!dev || !dev->attached)
+ dev = comedi_dev_get_from_minor(minor);
+ if (!dev)
return NULL;
- if (!try_module_get(dev->driver->module))
- return NULL;
+ if (dev->attached && try_module_get(dev->driver->module))
+ retval = dev;
+ else
+ retval = NULL;
+
+ if (retval == NULL)
+ comedi_dev_put(dev);
- return dev;
+ return retval;
}
EXPORT_SYMBOL_GPL(comedi_open);
@@ -63,6 +67,7 @@ int comedi_close(struct comedi_device *d)
struct comedi_device *dev = (struct comedi_device *)d;
module_put(dev->driver->module);
+ comedi_dev_put(dev);
return 0;
}
--
1.8.4.2
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