[LU-17929] Improve ptlrpc error reporting

• Type: Improvement
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.16.0
• Severity: 3
• Assignee: Aurelien Degremont
• Reporter: Aurelien Degremont

Description

Request allocation code in PTLRPC returns NULL on error and callers assume this is due to the system being out of memory.

Actually, there are multiple reasons this could fail like GSS error or failure to reconnect from an IDLE state. So let's improve that, making ptlrpc_request_alloc_pack() returns the actual error that will be bumped to the caller and likely the user-space, making debugging easier instead of always falsely return "System is out of memory" which is wrong most of the time.