From 544fd379ff8537ee2d48a4322aec854f2574fb46 Mon Sep 17 00:00:00 2001
From: Somesh Bhalsing <someshbhalsing@Velotios-MacBook-Air.local>
Date: Tue, 8 Nov 2022 19:49:54 +0530
Subject: [PATCH] feat: qemu exploration

---
 .gitignore       |  2 ++
 qemu/commands.md | 67 ++++++++++++++++++++++++++++++++++++++++++++++++
 qemu/solution.md | 22 ++++++++++++++++
 3 files changed, 91 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 qemu/commands.md
 create mode 100644 qemu/solution.md

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..137617d
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+.DS_Store
+qemu/alpine*
diff --git a/qemu/commands.md b/qemu/commands.md
new file mode 100644
index 0000000..27380cd
--- /dev/null
+++ b/qemu/commands.md
@@ -0,0 +1,67 @@
+someshbhalsing@Velotios-MacBook-Air k8s-dev-training % mkdir qemu
+
+someshbhalsing@Velotios-MacBook-Air k8s-dev-training % cd qemu 
+
+<!-- Create an empty qcow -->
+someshbhalsing@Velotios-MacBook-Air qemu % qemu-img create -f qcow2 alpine.qcow2 8G 
+Formatting 'alpine.qcow2', fmt=qcow2 cluster_size=65536 extended_l2=off compression_type=zlib size=8589934592 lazy_refcounts=off refcount_bits=16
+
+<!-- start the qemu with alpine iso image and attach the alpine.qcow to it -->
+someshbhalsing@Velotios-MacBook-Air qemu % qemu-system-x86_64 -m 512 -boot d -cdrom alpine-standard-3.16.2-x86_64.iso -hda alpine.qcow2 -display default -vga virtio -machine type=q35
+
+<!-- boot the alpine vm -->
+someshbhalsing@Velotios-MacBook-Air qemu % qemu-system-x86_64 -m 512 -hda alpine.qcow2
+
+<!-- image info -->
+someshbhalsing@Velotios-MacBook-Air qemu % qemu-img info alpine.qcow2 
+image: alpine.qcow2
+file format: qcow2
+virtual size: 8 GiB (8589934592 bytes)
+disk size: 352 MiB
+cluster_size: 65536
+Format specific information:
+    compat: 1.1
+    compression type: zlib
+    lazy refcounts: false
+    refcount bits: 16
+    corrupt: false
+    extended l2: false
+
+<!-- create a snapshot -->
+someshbhalsing@Velotios-MacBook-Air qemu % qemu-img snapshot -c snapshot-1 alpine.qcow2
+
+<!-- list the snapshot -->
+someshbhalsing@Velotios-MacBook-Air qemu % qemu-img snapshot -l alpine.qcow2   
+Snapshot list:
+ID        TAG               VM SIZE                DATE     VM CLOCK     ICOUNT
+1         snapshot-1            0 B 2022-11-08 19:23:00 00:00:00.000          0
+
+<!-- create an image from block -->
+someshbhalsing@Velotios-MacBook-Air qemu % qemu-img create -f qcow2 -b alpine.qcow2 -F qcow2 alpine-copy.qcow2
+Formatting 'alpine-copy.qcow2', fmt=qcow2 cluster_size=65536 extended_l2=off compression_type=zlib size=8589934592 backing_file=alpine.qcow2 backing_fmt=qcow2 lazy_refcounts=off refcount_bits=16
+
+<!-- new image info -->
+someshbhalsing@Velotios-MacBook-Air qemu % qemu-img info alpine-copy.qcow2 
+image: alpine-copy.qcow2
+file format: qcow2
+virtual size: 8 GiB (8589934592 bytes)
+disk size: 196 KiB
+cluster_size: 65536
+backing file: alpine.qcow2
+backing file format: qcow2
+Format specific information:
+    compat: 1.1
+    compression type: zlib
+    lazy refcounts: false
+    refcount bits: 16
+    corrupt: false
+    extended l2: false
+
+<!-- apply a commit -->
+someshbhalsing@Velotios-MacBook-Air qemu % qemu-img commit alpine-copy.qcow2 
+Image committed.
+
+<!-- check the diff between two images -->
+someshbhalsing@Velotios-MacBook-Air qemu % qemu-img compare alpine.qcow2 alpine.qcow2 
+Images are identical.
+
diff --git a/qemu/solution.md b/qemu/solution.md
new file mode 100644
index 0000000..f6b88e5
--- /dev/null
+++ b/qemu/solution.md
@@ -0,0 +1,22 @@
+#### QEMU
+
+- free and open-source emulator
+- emulates the machine's processor through dynamic binary translation
+- provides a set of different hardware and device models for the machine
+- enables machine run a variety of guest operating systems.
+- better performance as compared to virtualbox
+
+#### QCOW2
+
+- file format used by the qemu images
+- delays allocation of storage until it is actually needed
+
+#### Virtual size vs Disk size
+
+- virtual size is the size chosen while creating the drive.
+- disk size is the size that is actully allocated
+
+#### Backing chain
+
+- chains and overlays are created for snapshotting the image.
+- make it possible to apply any particular snapshot OR merge multiple images with same backing chain.
\ No newline at end of file