[Libguestfs] virtdf outputs on host differs from df in guest

[Richard W.M. Jones]

On Thu, Jan 04, 2018 at 12:58:40PM +0800, Chen Fan wrote:
[In guest]
> python -c 'import os; s = os.statvfs ("/"); print s'
> posix.statvfs_result(f_bsize=4096, f_frsize=4096, f_blocks=5886149,
> f_bfree=4802342, f_bavail=4802342, f_files=23556096,
> f_ffree=23435372, f_favail=23435372, f_flag=4096, f_namemax=255)
> 
> python -c 'import os; s = os.statvfs ("/boot"); print s'
> posix.statvfs_result(f_bsize=4096, f_frsize=4096, f_blocks=127147,
> f_bfree=93815, f_bavail=93815, f_files=512000, f_ffree=511626,
> f_favail=511626, f_flag=4096, f_namemax=255)

[From the host via libguestfs]
> # guestfish --ro -d rpm-build-for-7.2 -i statvfs /
> 
> bsize: 4096
> frsize: 4096
> blocks: 5886149
> bfree: 4810534
> bavail: 4810534
> files: 23556096
> ffree: 23435372
> favail: 23435372
> fsid: 64513
> flag: 4097
> namemax: 255
> 
> # sudo guestfish --ro -d rpm-build-for-7.2 -i statvfs /boot
> bsize: 4096
> frsize: 4096
> blocks: 127147
> bfree: 100215
> bavail: 100215
> files: 512000
> ffree: 511626
> favail: 511626
> fsid: 2049
> flag: 4097
> namemax: 255

Was the guest quiescent and fully sync()d before you ran the python
commands?

In any case all that libguestfs is doing is executing the
statvfs(2) system call on a copy of the disk:

  https://github.com/libguestfs/libguestfs/blob/e6e23c4d77ee15779f833fd4fbe6c574940e85a4/daemon/statvfs.c#L52

So if there's any difference then it's something to do with the guest
kernel vs the host kernel calculations.

I wouldn't expect the numbers to be exactly the same, but libguestfs
doesn't alter the numbers, it just passes them through.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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