[Libguestfs] virt-df: ext2/3/4 statvfs(2) output changed between two recent Linux kernels (3.2.0)
[Jim, as coreutils developer, this might interest you]
In libguestfs we run some quite detailed checks of the output of the
statvfs system call for our tool "virt-df". I noticed that the output
of virt-df changed slightly.
Narrowing it down, the difference only happens between:
Fedora kernel 3.2.0-0.rc0.git4.1.fc17 (3rd Nov)
Fedora kernel 3.2.0-0.rc1.git2.1.fc17 (11th Nov)
With 3.2.0-0.rc0.git4.1.fc17, and all earlier versions, the output of
statvfs(2) on a freshly created 20M ext2 filesystem is:
bsize: 1024
frsize: 1024
blocks: 19827 <-- NB
bfree: 19655
bavail: 18631
files: 5136
ffree: 5125
favail: 5125
fsid: 1411286354856931562
flag: 4096
namemax: 255
With 3.2.0-0.rc1.git2.1.fc17, it changed to:
bsize: 1024
frsize: 1024
blocks: 19939 <-- NB
bfree: 19655
bavail: 18631
files: 5136
ffree: 5125
favail: 5125
fsid: -9088586685126948527
flag: 4096
namemax: 255
I am able to demonstrate the difference by keeping every other package
identical, and just booting the two different kernels. As far as I
know, everything else including e2fsprogs is completely identical.
Reproducer:
export FEBOOTSTRAP_KERNEL=/boot/vmlinuz-<version>
guestfish sparse /tmp/test.img 20M : run : \
mkfs ext2 /dev/sda : mount /dev/sda / : statvfs /
I tracked this down to the way the filesystem overhead is calculated.
It changed slightly in the commit below. The description seems to be
wrong; it seems to affect any filesystem going through the ext4 driver
(this driver is used for ext2 & ext3 in recent Fedora), and doesn't
appear to have anything to do with 'bigalloc'.
commit f975d6bcc7a698a10cc755115e27d3612dcfe322
Author: Theodore Ts'o <tytso(a)mit.edu>
Date: Fri Sep 9 19:00:51 2011 -0400
ext4: teach ext4_statfs() to deal with clusters if bigalloc is enabled
Rich.
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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