Re: [fuse-devel] unknown mount options

[Nikolaus R. <Nik...@ra...>]

On Feb 20 2017, Yue Li <yli-wUU9E3n5/m56...@pu...> wrote:
> hi Nikolaus,
>
>
> On 2/4/17 8:34 PM, Nikolaus Rath wrote:
>> On Feb 04 2017, Yue Li <yli-wUU9E3n5/m56...@pu...> wrote:
>>> On 2/4/17 3:17 PM, Nikolaus Rath wrote:
>>>> On Feb 02 2017, Yue Li <yli-wUU9E3n5/m56...@pu...> wrote:
>>>>> I'm currently using the fuse compiled from the repository, and I'm
>>>>> trying the options suggested in the release note:
>>>>>
>>>>> https://github.com/libfuse/libfuse/releases
>>>>>
>>>>> Here's command for mounting
>>>>>
>>>>>     sudo ./run  -omodules=subdir,subdir=/mnt/store ./mount -o allow_other
>>>>> -o clone_fd -o writeback_cache
>>>>>
>>>>> And it gave the error
>>>>>
>>>>> fuse: unknown option(s): `-o writeback_cache'
>>>>>
>>>>> Similarly, the max_write option, async_dio and a few others also could
>>>>> not be recognized. I'm using the passthrough.c example for the tests above.
>>>>>
>>>>> Is there any special function I need to call to use these options?
>>>>> Thanks!
>>>> These are (in general) not options that you can pass on the command line
>>>> to the filesystem, but options that the filesystem can internally pass
>>>> to libfuse.
>>>>
>>> Is there any example on passing these options? Or could you point to the
>>> corresponding functions for doing this?
>> That depends on the option. The recommended way to enable the writeback
>> cache is to set a flag in your file system's init() handler, see
>> eg. https://github.com/libfuse/libfuse/blob/master/test/test_write_cache.c#L46.
>>
>>
>> Is the documentation at
>> http://libfuse.github.io/doxygen/fuse__common_8h.html and
>> http://libfuse.github.io/doxygen/fuse__lowlevel_8h.html not clear?
>
> I'm following the documentations and example above to enable 
> writeback_cache.
>
> Currently I'm using the high level interfaces, and I did the following 
> in the init function to enable writeback_cache and async_dio:
>
> static void *myfs_init(struct fuse_conn_info *conn, struct fuse_config *cfg)
> {
>    (void) conn;
>    cfg->use_ino = 1;
>    conn -> want |= FUSE_CAP_WRITEBACK_CACHE;
>    conn -> want |= FUSE_CAP_ASYNC_DIO;
>    return NULL;
> }
>
> Is the above sufficient to turn on the options when using the high-level 
> APIs?

Yes, but note that you'll get an error if the kernel doesn't support the
requested capabilities. You can check what's supported by looking at
conn->capable.

> Then I'm trying to see how can I set the sizes for write() and read(). 
> In the your test code above, it seems you used fuse_opt_parse function 
> to set the size for write()? Is there any other way to set this 
> variable? Can I change member variables of conn to do so?

I think you want to adjust conn->max_write and conn->max_read in init().

> And how do we change the size of read() under async_dio?

Not sure. DIO means most of the kernel is bypassed, so you may not have
control over it.

Best,
-Nikolaus

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