Hi Henri, thanks for geting back to me. I had managed to get DD to work with
the cmd, but I had to locate the file discripter in the fd directory in proc (
dd if=/proc/self/fd/{fd} ). If im writing a tool in python is it expected for
the FD to be handeld in a similler fashion?
Kind Regards
- Alasdair King
Research Computing Specialist
University Information Services
Roger Needham Building
JJ Thompson Avenue
University of Cambridge
Cambridge
Email: [email protected]
Tel: +441223746559
> On 8 Nov 2017, at 12:54, Henri Doreau <[email protected]> wrote:
>
>> Hi I am looking to make use of the lhsmtool_cmd, and im having trouble
>> understanding the use of the FD(File Descripter) varable requierd by
>> the tool. Is there anyone that can assist with my understanding? I'v
>> had a look unsuccessfully and at some examples, as well as run the
>> example with DD.
>>
>> Kind Regards
>>
>> - Alasdair King
>
> Hi,
>
> The FD is a file descriptor (integer) where the subprocess (the command
> which is spawned by the copytool) can read or write - depending whether
> it is archiving or restoring - data in Lustre.
>
> It is opened by the parent process, which receives and processes
> requests from the coordinator and passed to the subcommand so that it
> does not have to re-open the file. Internally, it is provided by
> llapi_hsm_action_get_fd().
>
> Because we want to be able to invoke arbitrary commands, we cannot use
> the standard sendmsg/recvmsg to pass FDs between processes and instead
> rely on /proc/self/{fd} to work with commands that expect paths, like
> dd.
>
> Hope this makes sense
> Regards
>
> --
> Henri
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