The next four sections document the straight C interface to attributes, indices, queries, and file system information. Technically, these functions are part of the Kernel Kit—their definitions live in header files in be/kernel, and their code is in libroot.so.

These functions use a global error variable (an integer), called errno, to register errors. You can look at the errno value directly in your code after a file system function fails. Alternatively, you can use the errno() function which prints, to standard error, its argument followed by a system-generated string that describes the current state of errno.

• Each thread maintains its own errno variable.

• errno is only set if there's an error—it never indicates success.

• errno is never cleared. If call A fails and then you call B, C, and D, errno will still record the error from A.