Hello Samuel,
* Samuel Hall <[email protected]> [2016-01-25 00:54:06 +0100]:
> In the implementation described in the article VFS isn't used due to the
> fact, that VFS wasn't available in genode at that time. A comment of the
> libc_fuse plugin states:
>
> […]
>
> So does the current implementation, when using a FUSE fs via the libc
> plugin, require VFS?
Yes. If you look at the different FUSE file systems you will see that
all of them use '/dev/blkdev' [1] to access the block device. By now,
this block device is configured through the VFS configuration by using
the VFS block plugin, e.g.:
<libc ...>
<vfs>
...
<dir name="dev"> <block name="blkdev"/> </dir>
</vfs>
</libc>
So when the FUSE file system wants to access the block device, the libc
will query all its plugins and normally the VFS plugin will answer the
call.
[1] repos/libports/src/lib/fuse-ext2/init.cc:49
> Is there any more detailed information about the VFS in genode?
There is more information in the release notes, albeit somewhat
scattered.
> I am particularly interested in finding out how the flow of a FUSE call
> differs in genode compared to the "normal" call as shown in this graphic
> [1].
If your component uses libc_fuse it looks basically like this:
open(/foo)
↳ libc (plugin list)
↳ libc_fuse (plugin)
↳ fuse->op.open(/foo)
↳ “ext2_read_inode” …
Since this happens all in the component itself there is no context switch
necessary (however, a context switch might occur in the FUSE file system
backend if the block session is provided by another component).
> When using a FUSE based fs as a file system server as described in Josef's
> response, do any adjustments have to be made to the FUSE fs so it runs on
> genode?
It depends on the file system but generally speaking one mostly ends
up reimplementating the file systems main() function if it uses the
normal fuse event loop.
Regards
Josef
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