/usr/include/errmsg_int.h is in libowfat-dev 0.30-2ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 | #include <stdarg.h>
void errmsg_puts(int fd,const char* s);
void errmsg_flush(int fd);
void errmsg_start(int fd);
void errmsg_write(int fd,const char* err,const char* message,va_list list);
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