The getfsstat system call returns information about all mounted file systems. The buf argument is a pointer to
.Vt statfs structures, as described in statfs(2).
Fields that are undefined for a particular file system are set to -1. The buffer is filled with an array of fsstat structures, one for each mounted file system up to the byte count specified by bufsize. Note, the bufsize argument is the number of bytes that buf can hold, not the count of statfs structures it will hold.
If buf is given as NULL, getfsstat returns just the number of mounted file systems.
Normally flags should be specified as MNT_WAIT. If flags is set to MNT_NOWAIT, getfsstat will return the information it has available without requesting an update from each file system. Thus, some of the information will be out of date, but getfsstat will not block waiting for information from a file system that is unable to respond.
Upon successful completion, the number of fsstat structures is returned. Otherwise, -1 is returned and the global variable errno is set to indicate the error.
The getfsstat system call fails if one or more of the following are true: