signal to release an fd?

[Stef Bon]

2011/5/21 Rémi Denis-Courmont <remi at remlab.net>:
> Le samedi 21 mai 2011 21:03:58 Stef Bon, vous avez écrit :
>> Well, this issue does not only happen with a construction like mine.
>>
>> For example, when working on a document on a USB stick (or a partition
>> on a harddisk)  with LibreOffice for example, and you want to create another
>> filesystem on it.
>
> This does not strike me as a common occurence. And it would be far simpler to
> "fix" LibreOffice to only keep file descriptors open while loading/saving
> documents - if it is not already doing so.

According to me keeping a file open is not strange and should not be
fixed. You need a filedescriptor to set a lock. So while working a fd
should be set.

The way you suggest is not so good in multi user environments.

>
> USB mass storage gadget is the only real-life scenario that I've ever: to
> expose a block device via USB MSC, the device must be unmounted. So
> applications running on the USB gadget cannot it. This mostly affects handheld
> devices.
>
> Even then, that's more of a design bug. If you want to share the handheld
> filesystem over USB, you should use a higher level protocol that does not
> require raw block access, e.g. OBEX-FTP or PTP/MTP. That is also the only way
> to not be stuck with the crappy old VFAT filesystem format.
>

My target is not only a filesystem on a USB stick, but also a
partition on a harddisk, and you want to create a new filesystem on
it, or has a file open on a network share and about to close the
networkconnection.


>> It's a very good and gentle service to the average user to have a
>> mechanism which informs the app to do something, like for example a
>> dialog informing the user and asking what to do.
>
> And what do you suggest?

I'm not suggesting anything, just asking this is already possible. I
do not know everything, and maybe this is already possible. So just a
question.

You're right that it's not possible to pass the fd. Instead of that
the inode is sufficient, or the path.

The path is likely a candidate.

Well I do not know how app developers have to implement this. I think
it's a big plus to have this, instead of just closing the file
bluntly, losing data.

You can also think of the end of a session. When a app like swriter
has a file open with unsaved changes, it's a good thing to send a
message first (and wait for it to complete in reasonable period) and
then terminate the app.

Stef