(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.