• File I/O and copying

    From Steve Keller@21:1/5 to All on Fri Feb 8 12:39:48 2019
    I'd like to understand how file I/O is typically handled on todays PCs
    or servers running any modern Unix (*BSD, Linux, etc.).

    How much copying is involved when I read from a file using the read
    system call? And does this depend on alignment of my user space
    buffer that I read into?

    Can the I/O hardware and block device driver (maybe using DMA) copy
    directly to user space, and if so to any address or are there
    alignment constraints? Or is data copied to a kernel buffer first and
    then copied to user space?

    Steve

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