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Bruno Reis
Asked: 2014-07-04 10:19:43 +0800 CST

Does fsfreeze flush FS caches?

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If I run fsfreeze on a mounted filesystem, it will not be possible to perform new "write" operations on that FS until it is unfrozen, and "ongoing" writes should "complete".

Now, will fsfreeze also flush the FS caches, after it starts blocking new writes, and after it completes those ongoing writes, and before it returns? Can you point me to any authoritative source, please?

I've spent time reading the docs, but couldn't find this explicitly mentioned anywhere. The closest I find is "creates a stable image on disk" -- does this mean that it flushes the FS caches?

Thanks.

filesystems

1 Answers

  1. Best Answer

    fsfreeze uses the FIFREEZE ioctl. Here is the kernel function call chain:

    1. ioctl_fsfreeze()
    2. freeze_super()
    3. sync_filesystem()

    From the comment above the sync_filesystem() function: "[w]rite out and wait upon all dirty data associated with this superblock [filesystem]. Filesystem data as well as the underlying block [will be written."

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