Add note about benchmarking.

[libguestfs-talks.git] / 2019-fosdem / paper / fosdem-rjones-better-loopback-paper.tex

diff --git a/2019-fosdem/paper/fosdem-rjones-better-loopback-paper.tex b/2019-fosdem/paper/fosdem-rjones-better-loopback-paper.tex
index 6a0e47f..f6bcf6b 100644 (file)
--- a/2019-fosdem/paper/fosdem-rjones-better-loopback-paper.tex
+++ b/2019-fosdem/paper/fosdem-rjones-better-loopback-paper.tex
@@ -1,3 +1,10 @@
+% TODO:
+% Can we use nbdkit to test kernel limits?
+%  - max size (already mostly covered)
+%  - max number of partitions:
+%      try 128 partitions with GPT
+%      then modify GPT code to try > 128 partitions
+
 \documentclass[12pt,a4paper]{article}
 \usepackage[utf8x]{inputenc}
 \usepackage{parskip}
@@ -183,15 +190,75 @@ gone, making this very useful for testing filesystems.
 
 \section{Concatenating files into a partitioned disk}
 
-\textit{In the talk this section will talk about creating a virtual
-  disk with a virtual partition table using the nbdkit
-  ``partitioning'' plugin.}
+Whereas loopback mounts are limited to a single file, there are
+several nbdkit plugins for combining files.  One of them is called the
+``partitioning'' plugin, and it turns partitions into disk images:
+
+\begin{verbatim}
+$ nbdkit partitioning \
+         boot.img \
+         swap.img \
+         root.img
+\end{verbatim}
+
+This time I'll use \texttt{guestfish} to examine this virtual disk:
+
+\begin{verbatim}
+$ guestfish --format=raw -a nbd://localhost -i
+
+Welcome to guestfish, the guest filesystem shell for
+editing virtual machine filesystems and disk images.
+
+Type: ‘help’ for help on commands
+      ‘man’ to read the manual
+      ‘quit’ to quit the shell
+
+Operating system: Fedora 26 (Twenty Six)
+/dev/sda3 mounted on /
+/dev/sda1 mounted on /boot
+
+><fs> list-filesystems 
+/dev/sda1: ext4
+/dev/sda2: swap
+/dev/sda3: xfs
+\end{verbatim}
+
+You can see that the NBD disk contains three
+partitions\footnote{\texttt{/dev/sdX} inside libguestfs is equivalent
+  to \texttt{/dev/nbd0} on the host}.
 
 
 \section{Mounting a VMware VMDK file}
 
-\textit{In the talk this section will talk about modifying VMware VMDK
-  files using the nbdkit ``vddk'' plugin.}
+VMware VMDK disk images are difficult to open on Linux machines.
+VMware provides a proprietary library to handle them, and nbdkit has a
+plugin to handle this library (the plugin is free software, but the
+VMware library that it talks to is definitely not).  We can use this
+to loopback mount VMDK files:
+
+\begin{verbatim}
+# nbdkit vddk file=TestLinux-disk1.vmdk
+# nbd-client -b 512 localhost 10809 /dev/nbd0
+\end{verbatim}
+
+This disk image contains two partitions and several logical volumes.
+The Linux kernel finds them all automatically:
+
+\begin{verbatim}
+# file -bsL /dev/nbd0p1
+Linux rev 1.0 ext4 filesystem data, UUID=9d1d5cb7-b453-48ac-b83b-76831398232f (needs journal recovery) (extents) (huge files)
+# file -bsL /dev/nbd0p2
+LVM2 PV (Linux Logical Volume Manager), UUID: bIY2oM-CgAN-npqG-gItS-WY6e-wO7d-L6G3Bv, size: 8377444864
+# ls /dev/vg_testlinux/
+lv_root  lv_swap
+\end{verbatim}
+
+You can read and write to VMDK files this way:
+
+\begin{verbatim}
+# mount /dev/vg_testlinux/lv_root /mnt
+# touch /mnt/hello
+\end{verbatim}
 
 
 \section{Testing a RAID array}