(read_filesystem_list):

(read_filesystem_list):
Don't leak memory on failure.
Don't create a dummy struct mount_entry entry;
use the address-of-the-tail-address method instead.
Preserve errno if possible on failure, setting it to 0 if inapplicable.
Close file descriptor leak if the F_SETLKW failed.
Report an error if SVR4 lock file cannot be opened for some reason
other than a nonexistent lock file.