MFV r323790: 8567 Inconsistent return value in zpool_read_label
illumos/illumos-gate@c861bfbd77c4ae780a0341e9cb6926d8b74341cf
https://github.com/illumos/illumos-gate/commit/c861bfbd77c4ae780a0341e9cb6926d8b74341cf
https://www.illumos.org/issues/8567
If fstat64 fails, pread64 fails, or the label is unintelligible, zpool_read_label will return 0. But if malloc fails, it will return -1. For consistency, it should always return -1 on failure or 0 on success.
Reviewed by: Prakash Surya <prakash.surya@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Author: Alan Somers <asomers@gmail.com>
MFC after: 2 weeks