What does errno 54 (EBADRQC) mean?

EBADRQC

The invalid field is the request code

EBADRQC is defined as errno 54 in the illumos Solaris-compatible header. Oracle's errno catalog names it invalid request code. Unlike EBADR, whose noun is a request descriptor, EBADRQC points at the operation selector or command code carried by a legacy interface.

Oracle does not document a general modern Solaris syscall that must return this errno, and POSIX does not define the name. It should therefore be interpreted in the contract of the component that emitted it. In an old driver or protocol API, the relevant field may be an ioctl-like command, a private request number, or a compatibility-layer opcode.

Checks that preserve the distinction

• Log the numeric request or command value presented to the failing component and the version of that component's interface.
• Verify structure/version negotiation before assuming permissions or resource exhaustion; an unknown opcode is a different failure class.
• Do not rewrite EBADRQC as EINVAL in a decoder unless the target API explicitly defines that mapping.

References

• Oracle Solaris intro(2) errno catalog
• illumos sys/errno.h ABI definitions
• POSIX Issue 8 errno.h

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