[GSoC project] Implementation of ISO9660 filesystem
chrisj at rtems.org
Tue Apr 5 11:54:22 UTC 2011
On 5/04/11 9:37 PM, Sebastian Huber wrote:
> On 04/05/2011 01:01 PM, Chris Johns wrote:
>> On 5/04/11 4:42 PM, Sebastian Huber wrote:
>>> On 04/05/2011 12:36 AM, Chris Johns wrote:
>>>> On 4/04/11 9:22 PM, Sebastian Huber wrote:
>>>>> one of the big problems with removable media and RTEMS is that
>>>>> currently it is
>>>>> impossible to unmount a file system in use. This is a fundamental
>>>>> flaw in the
>>>>> RTEMS file system layer. We should address this somehow in this
>>>>> project (we
>>>>> need some sort of reference counting).
>>>> I see the need to be able to forcible remove a mount and any open files
>>>> return an error when accessed how-ever the unmount call should be aloud
>>>> to fail if the media is valid and in use and call is not forced.
>>> Yes. The problem is that there is currently no way to figure out if a
>>> system is in use or not. With in use I mean that there exist some
>>> nodes that
>>> belong to the file system. The nodes may be not related to a file
>>> We have also root and current directory nodes (chroot() and chdir()).
>> In the current code it attempts to unmount and if it fails it knows the
>> file system is in use.
> If you call unmount() you must ensure that the file system is not in use,
> otherwise you will likely corrupt the system (e.g. heap memory use after free).
> The current EBUSY checks in unmount() are insufficient.
The file system should be able to tell if it is in use. For a forced
unmount any files would need to be flagged in the iop that the file is
no longer valid.
> We need some sort of
> reference counting and we have to protect the file system node consumer and
> producer code from concurrent access.
We need something here for other reasons as well.
>> What is the use case for knowing the file system is in use and not
>> attempting to unmount and seeing if it fails ?
> The unmount() API is not the problem.
It is if you want to force an unmount.
More information about the users