libguestfs launch times

Indulge me while a make a “note to self” about efforts to reduce the time taken by guestfs_launch which boots up the libguestfs appliance.

Time (s)
Operation

2s

Create supermin appliance: This has crept up over time from originally taking about 1/5th of a second to around 2s. Needs attention. Fixed see this [...]

Half-baked ideas: inject syscalls into virtual machines

For more half-baked ideas, see my “ideas” tag.
After we wrote virt-df and later libguestfs, what customers were asking me about was to be able to read out of /proc and /sys in a running virtual machine.
Of course that’s not possible with libguestfs. libguestfs reads the filesystem. /proc is a synthetic “filesystem” that only [...]

How does mount load the right kernel module?

On any recent Linux distro, you can mount any filesystem type directly. For example:

# dd if=/dev/zero of=/tmp/test.img bs=4k count=4096
# mkfs.xfs /tmp/test.img
# mount -v -o loop /tmp/test.img /mnt/tmp

The mount command works even though I didn’t have the xfs.ko kernel module loaded, and I didn’t tell mount that it’s xfs.
How does it do that? I [...]

Size of RPM dependencies

Continuing the theme of minimal Fedora installs, I had a go at visualizing RPM dependencies and the size of those dependencies.
This problem is harder than I thought. The pretty filelight diagrams in my last post are possible because filesystems are simple trees (if you discount hard links).
However package dependencies are directed graphs, often containing [...]