Add `comedi_open_from(path, from)` and `comedi_close_from(dev, from)` as variants of the existing `comedi_from(path)` and `comedi_close(dev)`. The additional `from` parameter is a minor device number that tells the function that the COMEDI device is being opened or closed from another COMEDI device if the value is in the range [0, `COMEDI_NUM_BOARD_MINORS`-1]. In that case the function will refuse to open the device if it would lead to a chain of devices opening each other. (It will also impose a limit on the number of simultaneous opens from one device to another because we need to count those.) The new functions are intended to be used by the "comedi_bond" driver, which is the only driver that uses the existing `comedi_open()` and `comedi_close()` functions. The new functions will be used to avoid some possible deadlock situations. Replace the existing, exported `comedi_open()` and `comedi_close()` functions with inline wrapper functions that call the newly exported `comedi_open_from()` and `comedi_close_from()` functions. Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Link: https://patch.msgid.link/20251027153748.4569-2-abbotti@mev.co.uk Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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