Squid internals

The disk interface (src/disk.c)
A hold-over from a half-integrated async disk IO implementation
Functions to manipulate disk FDs
Open a file
fd = file_open(path, mode)
Close a file
file_close(fd)
Write to a file
file_write(fd, offset, buf, len, callback, callbackdata, freefunc)
Read from a file
file_read(fd, buf, req_len, offset, callback, callbackdata)

Note that these functions are going away!