note/noteram: add FIONREAD ioctl to report unread buffer size

[Kaben123]

Add handling for the FIONREAD ioctl in noteram_ioctl to return the number of unread bytes in the circular note buffer (noteram_unread_length()). Validate the argument pointer and return -EINVAL if it is NULL.

Note: Please adhere to Contributing Guidelines.

Summary

This patch adds support for the FIONREAD ioctl command in the noteram driver to allow user-space to query the number of unread bytes in the circular note buffer.

Motivation

User-space consumers of /dev/note/ram can benefit from being able to query the available unread size for efficient reads without blocking or to size buffers appropriately.

What was changed

• drivers/note/noteram_driver.c
  • Added handling for FIONREAD in noteram_ioctl() to return the result of noteram_unread_length() when a valid pointer is passed.

Impact

• Functional behavior: Adds a new ioctl handler; no behavior change to existing functionality.
• API/ABI: Adds support for a commonly used ioctl (FIONREAD) on the device node.
• Risks: Minimal. The added code verifies arg and returns -EINVAL for null pointer.

Testing

• Compiled and ran on development board. Verified ioctl(fd, FIONREAD, &size) returns expected available bytes.