Ecila comes back through the mirror

• When all I/O requests came from the disk (or earlier - if all data was in the cache), the read request copies the data to the user buffer(s).
  • A read() will copy into a single buffer.
  • A readv will copy into multiple buffers.
• Note: it is allowed to return only partial data!
  • To simplify the code handling reads in the kernel (or the driver)
  • To simplify handling of signals received in the middle of the system call.
• Thus: always check how many bytes were actually read, and don't assume a premature return is an error!
• (the same is true for writes too!).

Originally written by guy keren