[LU-5252] HSM: update fifo event API and code

• Type: Bug
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.7.0, Lustre 2.5.3
• Affects Version/s: Lustre 2.5.1
• Labels: HSM patch
• Severity: 3
• Assignee: James Nunez (Inactive)
• Reporter: Frank Zago (Inactive)

Description

Neither llapi_hsm_register_event_fifo() nor
llapi_hsm_unregister_event_fifo() take a const as their argument. This
lead to the following compilation warning when a caller is using a
const char *:

    
      ... warning: passing argument 1 of ‘llapi_hsm_register_event_fifo’ discards ‘const’ qualifier from pointer target type [enabled by default]
       rc = llapi_hsm_register_event_fifo(lustre_fifo_event);
       ^
      ... note: expected ‘char *’ but argument is of type ‘const char *’
      extern int llapi_hsm_register_event_fifo(char *path);

Also, llapi_hsm_event_fd is local, so make it static.

And finally, do not unconditionally delete the HSM event fifo.
The lustreapi HSM library will use a pipe if it already exists.
However the deregistration will unconditionally delete that pipe,
which is not correct.

An admin may want to create the pipe with certain rights/ownership,
which the llapi_hsm_register_event_fifo() doesn't allow. In that case,
llapi_hsm_unregister_event_fifo() should not delete it.

Patches to follow.