Kernel Tools

Here are some guides about the tools we daily used in the kernel world.

git#

In progress

qemu#

tutorial#

We have a video(in chinese) about how to use the basic function of qemu.

snapshot#

QEMU Snapshot Feature

Background: The desire is for QEMU to have a snapshot feature, allowing the saving of the current state when a bug occurs. This snapshot can be accessed later for debugging purposes.

1. Creating a QCOW2 Image with qemu-img:

   • Use the command qemu-img create -f qcow2 test.qcow2 32M to create an image.
   • test.qcow2 is the desired name for the image, and the size can be specified as needed, here it’s set to 32M.
   • The common error “Error: No block device can accept snapshots” usually occurs due to the absence of an image.

2. Updating QEMU Command:

   • Modify the existing QEMU command by adding -drive if=none,format=qcow2,file=test.qcow2.

3. Saving a Snapshot:

   • To save a snapshot when a bug occurs or when needed, use Ctrl+A C to bring up the QEMU monitor, then use savevm snapshot1 to save the snapshot, where snapshot1 is the desired name for the snapshot.
   • Use info snapshots in the QEMU monitor to view all current snapshot information.

4. Loading a Snapshot and Debugging with GDB:

   • On top of the QEMU command with the -drive option, use the -loadvm snapshot1 option to load the snapshot.
   • This can be combined with GDB for debugging.

emails#

Use mutt to send/recieve the mails and use b4 to fetch the patches in the email list.

mutt#

Mutt is a simple command-line tool that can be used in conjunction with Git to send and reply to emails for community interactions. Its popularity is due to its straightforward configuration.

Here is a config file, you can put it in the ~/.muttrc to configure you mutt.

# ================  SMTP  ====================
set smtp_url =  # smtp_url
set smtp_pass =  "" # your password here, find it in the email vendor
set ssl_force_tls = yes # Require encrypted connection

# ================  Composition  ====================
# set editor = vim
set edit_headers = yes  # See the headers when editing
set charset = UTF-8     # value of $LANG; also fallback for send_charset
# Sender, email address, and sign-off line must match
unset use_domain        # because joe@localhost is just embarrassing
set realname = "name" # Change this to your name
set from = "email" # Change this to your email
set use_from = yes

ignore *
unignore From: Date: To: Cc: Subject: Reply-To: List-ID: Message-ID: In-Reply-To:
hdr_order From: Date: To: Cc: Subject: Reply-To: List-ID: Message-ID: In-Reply-To:

set wrap=80
set text_flowed
set editor="vim -c 'set formatoptions+=w' -c 'set textwidth=72'"

Tips:

1. When sending emails to the kernel community, keep in mind:

• Emails should not exceed 80 characters per line for easier reading.
• The format of the email should be plain text without any formatting. This is because reading formatted content requires additional email size, and command-line clients may not display rich text formats correctly.
• Use in-line replies instead of top replies.

2. It’s advisable to cc (carbon copy) yourself when sending emails to the kernel community. This helps you better understand how your sent email looks and confirms its successful delivery.
3. Remember to include a reply when responding to emails.
4. If you encounter any problems, you can always ask the email system administrator for help.

b4#

Using b4 can quickly apply community patches to your Linux source code:

1. Install b4:

   • Run pip3 install b4 --user to install b4.

2. Obtain the patch:

   • Use b4 am or b4 mbox to get a patch. For example, you can run: b4 am CANiq72nyTdfBQDrBNOV7MEhpbwM3hYEeyaVZgRpMv8xFkLBwdw@mail.gmail.com

3. Merge the patch using git:

   • Use git am followed by the patch file, like git am xx.mbox, to merge the patch into your code.