title: How to disable the filesystem cache on the root device?
body: <p>I've got an ARM virtual machine running on top of KVM/QEMU, with a file mounted as the root filesystem. The VM doesn't have networking, so NFS mounting the root is out of the question. I am testing a particular transport mechanism for IO, so I'm kind of stuck with what I've got.</p>
  
  <p>I want to send files into the guest, so I'd like to mount the file on the host, write things to it, and then unmount it to force a flush. The contents of the filesystem are trivial, and I have a backup, so I have no problem with corruption. Likewise, performance is not an issue.</p>
  
  <p>The problem is, when I do this mount-write-unmount thing, the guest never sees the file. I'm guessing this is a result of the kernel's filesystem cache, and that when I do ls, the file isn't there. I'm guessing the metadata concerning the filesystem are cached in memory, and the updates to the filesystem never appear.</p>
  
  <p>I'm guessing if I disable filesystem caching, then all reads will be forced to disk, causing the filesystem to be hit, and my file to appear. Any tips? </p>