Re: [LSF/MM/BPF TOPIC] block drivers in user space

[Damien Le Moal <damien.lemoal@opensource.wdc.com>]

On 2/22/22 04:59, Gabriel Krisman Bertazi wrote:
> I'd like to discuss an interface to implement user space block devices,
> while avoiding local network NBD solutions.  There has been reiterated
> interest in the topic, both from researchers [1] and from the community,
> including a proposed session in LSFMM2018 [2] (though I don't think it
> happened).
> 
> I've been working on top of the Google iblock implementation to find
> something upstreamable and would like to present my design and gather
> feedback on some points, in particular zero-copy and overall user space
> interface.
> 
> The design I'm pending towards uses special fds opened by the driver to
> transfer data to/from the block driver, preferably through direct
> splicing as much as possible, to keep data only in kernel space.  This
> is because, in my use case, the driver usually only manipulates
> metadata, while data is forwarded directly through the network, or
> similar. It would be neat if we can leverage the existing
> splice/copy_file_range syscalls such that we don't ever need to bring
> disk data to user space, if we can avoid it.  I've also experimented
> with regular pipes, But I found no way around keeping a lot of pipes
> opened, one for each possible command 'slot'.
> 
> [1] https://dl.acm.org/doi/10.1145/3456727.3463768

This is $15 for non ACM members... Any public download available ?

> [2] https://www.spinics.net/lists/linux-fsdevel/msg120674.html
> 


-- 
Damien Le Moal
Western Digital Research