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Two kernel journeys: reading a file from storage and sending bytes over a network device.

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Trace a read syscall through VFS and ext4; a cache miss reaches NVMe, while returned bytes travel back through the page cache.

System map8 components · 9 connections
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Linux kernel architectureThe system-call gate sits at the upper left. The storage path runs across the center to NVMe; the networking path drops toward the socket and device stack. Return-data arrows show bytes traveling back toward user space.file descriptor, user …struct file, kiocb, io…mapping, file position…bio with disk sectors …request tag, NVMe comm…copied bytes, updated …System-callgateVirtualfilesystemext4filesystemBlockmulti-queuePage cacheNVMe driverSocket and TCPNetworkdevice core
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Terms, in plain English

System callA controlled transition that lets a user-space program request privileged kernel work.

How to study this repo

  1. 1
    Begin at a syscall boundary

    Compare arch/x86/entry/common.c with fs/read_write.c to separate CPU entry mechanics from generic kernel policy.

  2. 2
    Follow one cache miss

    Trace the structs passed from filemap code toward blk-mq and note where a file offset becomes storage sectors.

  3. 3
    Contrast files with sockets

    Read net/socket.c and net/core/dev.c and identify the equivalent boundary, buffering, and driver handoff concepts.