thr3ads.net - Libguestfs - Re: [Libguestfs] virtdf outputs on host differs from df in guest [Jan 2018]

If this information is useful, please help other people find it:
Share via:

陈帆

2018-Jan-04 13:21 UTC

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

hi Jones, Thanks for your reply.


At 2018-01-04 19:41:27, "Richard W.M. Jones" <rjones@redhat.com>
wrote:>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?

yes, almost the guest is quiescent, and after invoke sync(), the results have no
different.

>
>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 saw that when doing virt-df, virt-df created a  temporary VM with the host
kernel, so I
recreate a temporary QEMU VM with command line: 
/usr/libexec/qemu-kvm -cpu host -m 1024 -nographic -kernel
/var/tmp/.guestfs-0/appliance.d/kernel -initrd
/var/tmp/.guestfs-0/appliance.d/initrd -append "console=ttyS0 root=/dev/vda
guestfs_rescue=1" -device virtio-blk-pci,drive=disk0 -drive
file=/var/tmp/.guestfs-0/appliance.d/root,id=disk0,if=none -device virtio-serial
-chardev socket,id=charchannel0,path=/tmp/a,server,nowait -device
virtserialport,nr=1,chardev=charchannel0,id=channel0,name=org.libguestfs.channel.0
-device virtio-blk-pci,drive=disk1 -drive
file=/srv/imgs/centos-7.2.qcow2,if=none,id=disk1
then the console showing:><rescue> mount /dev/vdb1 /sysroot/[   72.552185] SGI XFS with ACLs, security attributes, no debug enabled
[   72.568377] XFS (vdb1): Mounting V4 Filesystem
[   73.379679] XFS (vdb1): Starting recovery (logdev: internal)
[   73.406398] XFS (vdb1): Ending recovery (logdev:
internal)><rescue> statvfs
bash: statvfs: command not found><rescue> stat -f /sysroot  File: "/sysroot"
    ID: fd1100000000 Namelen: 255     Type: xfs
Block size: 4096       Fundamental block size: 4096
Blocks: Total: 127147     Free: 93815      Available: 93815
Inodes: Total: 512000     Free: 511626



here the mount /dev/vdb1 device is the /boot partition from my guest, we can saw
that
the free blocks are the same as python command, so I think the host kernel does
not affect the result.
if I am wrong, pls correct me :)


Thanks,
Chen





>
>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
>Read my programming and virtualization blog: http://rwmj.wordpress.com
>Fedora Windows cross-compiler. Compile Windows programs, test, and
>build Windows installers. Over 100 libraries supported.
>http://fedoraproject.org/wiki/MinGW

Richard W.M. Jones

2018-Jan-04 16:22 UTC

head link

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

To summarise:
>[In guest]
> 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]
> # 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
[In virt-rescue]> Block size: 4096       Fundamental block size: 4096
> Blocks: Total: 127147     Free: 93815      Available: 93815
> Inodes: Total: 512000     Free: 511626
The block stats are the same as the "in guest" results above,
but slightly different from libguestfs.

		- * - * - * -

I wanted to see if I could reproduce this with a very simple and
reproducible example.  I made the assumption that this guest is using XFS.

(1) Make an XFS filesystem and use libguestfs to query the statvfs:

$ guestfish -N fs:xfs -m /dev/sda1 statvfs /
bsize: 4096
frsize: 4096
blocks: 24713
bfree: 23347
bavail: 23347
files: 51136
ffree: 51133
favail: 51133
fsid: 2049
flag: 4096
namemax: 255

(2) Open the same disk image in virt-rescue and examine with stat
command:

$ virt-rescue -a test1.img><rescue> mount /dev/sda1 /sysroot
><rescue> stat -f /sysroot  File: "/sysroot"
    ID: 80100000000 Namelen: 255     Type: xfs
Block size: 4096       Fundamental block size: 4096
Blocks: Total: 24713      Free: 23347      Available: 23347
Inodes: Total: 51136      Free: 51133


In this case the numbers are the same ...

I would really like a bit more information though:

(a) Are you using XFS or another filesystem?

(b) Can you make a small independent reproducer like mine above?

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
libguestfs lets you edit virtual machines.  Supports shell scripting,
bindings from many languages.  http://libguestfs.org

陈帆

2018-Jan-07 12:11 UTC

head link

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

hi Jones,


Sorry for the late reply. when I used your method to execute command:
 $guestfish -N fs:xfs -m /dev/sda1 statvfs /
libguestfs: error: mkfs: xfs: /dev/sda1: mkfs.xfs: No such file or directory
guestfish: error creating prepared disk image 'fs:xfs' on
'test1.img': failed to create filesystem (xfs): mkfs: xfs: /dev/sda1:
mkfs.xfs: No such file or directory

does I need to rebuild the iniramfs to include mkfs.xfs, is this the root reason
that cause the different numbers ?
then I used virt-rescure method , the filesystem type was
ext2/ext3:><rescue> mount /dev/sda1 /sysroot/mount: /dev/sda1 is write-protected, mounting read-only
mount: unknown filesystem type '(null)'><rescue> stat -f /sysroot  File: "/sysroot"
    ID: ab0d9f3277e010fd Namelen: 255     Type: ext2/ext3
Block size: 4096       Fundamental block size: 4096
Blocks: Total: 1032112    Free: 941307     Available: 888879
Inodes: Total: 262144     Free: 250996><rescue> 

Thanks,
Chen





At 2018-01-05 00:22:46, "Richard W.M. Jones" <rjones@redhat.com>
wrote:>To summarise:
>
>>[In guest]
>> 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]
>> # 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
>
>[In virt-rescue]
>> Block size: 4096       Fundamental block size: 4096
>> Blocks: Total: 127147     Free: 93815      Available: 93815
>> Inodes: Total: 512000     Free: 511626
>
>The block stats are the same as the "in guest" results above,
>but slightly different from libguestfs.
>
>		- * - * - * -
>
>I wanted to see if I could reproduce this with a very simple and
>reproducible example.  I made the assumption that this guest is using XFS.
>
>(1) Make an XFS filesystem and use libguestfs to query the statvfs:
>
>$ guestfish -N fs:xfs -m /dev/sda1 statvfs /
>bsize: 4096
>frsize: 4096
>blocks: 24713
>bfree: 23347
>bavail: 23347
>files: 51136
>ffree: 51133
>favail: 51133
>fsid: 2049
>flag: 4096
>namemax: 255
>
>(2) Open the same disk image in virt-rescue and examine with stat
>command:
>
>$ virt-rescue -a test1.img
>><rescue> mount /dev/sda1 /sysroot
>><rescue> stat -f /sysroot
>  File: "/sysroot"
>    ID: 80100000000 Namelen: 255     Type: xfs
>Block size: 4096       Fundamental block size: 4096
>Blocks: Total: 24713      Free: 23347      Available: 23347
>Inodes: Total: 51136      Free: 51133
>
>
>In this case the numbers are the same ...
>
>I would really like a bit more information though:
>
>(a) Are you using XFS or another filesystem?
>
>(b) Can you make a small independent reproducer like mine above?
>
>Rich.
>
>-- 
>Richard Jones, Virtualization Group, Red Hat
http://people.redhat.com/~rjones
>Read my programming and virtualization blog: http://rwmj.wordpress.com
>libguestfs lets you edit virtual machines.  Supports shell scripting,
>bindings from many languages.  http://libguestfs.org

Possibly Parallel Threads

Search for more possibly parallel threads

Libguestfs - Jan 2018 - Re: virtdf outputs on host differs from df in guest

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

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

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

Possibly Parallel Threads