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Review and link kernel_module/user examples to README
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Ciro Santilli
90
README.adoc
90
README.adoc
@@ -4863,9 +4863,6 @@ sendkey shift-pgdown
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===== Ctrl Alt Del
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* https://superuser.com/questions/193652/does-linux-have-a-ctrlaltdel-equivalent/1324415#1324415
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* https://unix.stackexchange.com/questions/42573/meaning-and-commands-for-ctrlaltdel/444969#444969
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Reboot guest:
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....
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@@ -4952,9 +4949,12 @@ ever reaches the kernel tty layer, and it's up to the program
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to decide what to do with it.
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....
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===== SysRq
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Bibliography:
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https://en.wikipedia.org/wiki/Magic_SysRq_key
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* https://superuser.com/questions/193652/does-linux-have-a-ctrlaltdel-equivalent/1324415#1324415
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* https://unix.stackexchange.com/questions/42573/meaning-and-commands-for-ctrlaltdel/444969#444969
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===== SysRq
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We cannot test these actual shortcuts on QEMU since the host captures them at a lower level, but from:
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@@ -5004,6 +5004,8 @@ The bitmask is documented at:
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less linux/Documentation/admin-guide/sysrq.rst
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....
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Bibliography: https://en.wikipedia.org/wiki/Magic_SysRq_key
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==== TTY
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In order to play with TTYs, do this:
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@@ -5076,6 +5078,8 @@ Identify the current TTY with the command:
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tty
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....
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Bibliography:
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* https://unix.stackexchange.com/questions/270272/how-to-get-the-tty-in-which-bash-is-running/270372
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* https://unix.stackexchange.com/questions/187319/how-to-get-the-real-name-of-the-controlling-terminal
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* https://unix.stackexchange.com/questions/77796/how-to-get-the-current-terminal-name
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@@ -5133,7 +5137,7 @@ insmod /kthread.ko
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and switch between virtual terminals, to understand that the dmesg goes to whatever current virtual terminal you are on, but not the others, and not to the serial terminals.
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See also:
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Bibliography:
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* https://serverfault.com/questions/119736/how-to-enable-multiple-virtual-consoles-on-linux
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* https://github.com/mirror/busybox/blob/1_28_3/examples/inittab#L60
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@@ -5197,7 +5201,7 @@ Instead, the shell appears on `/dev/tty7`.
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If you run in <<graphic-mode>>, then you get a Penguin image for <<number-of-cores,every core>> above the console! https://askubuntu.com/questions/80938/is-it-possible-to-get-the-tux-logo-on-the-text-based-boot
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This is due to the `CONFIG_LOGO=y` option which we enable by default.
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This is due to the link:https://github.com/torvalds/linux/blob/v4.17/drivers/video/logo/Kconfig#L5[`CONFIG_LOGO=y`] option which we enable by default.
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`reset` on the terminal then kills the poor penguins.
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@@ -5350,7 +5354,7 @@ When I build it on Ubuntu 18.04 host, it does not generate any executable, so I'
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=== Linux kernel testing
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https://stackoverflow.com/questions/3177338/how-is-the-linux-kernel-tested
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Bibliography: https://stackoverflow.com/questions/3177338/how-is-the-linux-kernel-tested
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==== LTP
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@@ -5417,8 +5421,6 @@ Some QEMU specific features to play with and limitations to cry over.
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=== Snapshot
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https://stackoverflow.com/questions/40227651/does-qemu-emulator-have-checkpoint-function/48724371#48724371
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QEMU allows us to take snapshots at any time through the monitor.
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You can then restore CPU, memory and disk state back at any time.
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@@ -5493,6 +5495,8 @@ And the output is `0`.
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Our setup does not allow for snapshotting while using <<initrd>>.
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Bibliography: https://stackoverflow.com/questions/40227651/does-qemu-emulator-have-checkpoint-function/48724371#48724371
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==== Snapshot internals
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Snapshots are stored inside the `.qcow2` images themselves.
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@@ -5918,8 +5922,6 @@ Rationale: we found out that the kernels that build for `qemu -M versatilepb` do
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At the same time, we also found out that Versatile Express (`vexpress`) does support armv7, so maybe we could port it over, but I had lost interest at that point, and decided to just go with the simpler `-M virt` machine instead.
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https://stackoverflow.com/questions/28315265/how-to-add-a-new-device-in-qemu-source-code/44612957#44612957
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Uses:
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* `hw/misc/lkmc_platform_device.c` minimal device added in our QEMU fork to `-M versatilepb`
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@@ -5951,6 +5953,8 @@ The IRQ number `34` was found by on the dmesg after:
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insmod /platform_device.ko
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....
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Bibliography: https://stackoverflow.com/questions/28315265/how-to-add-a-new-device-in-qemu-source-code/44612957#44612957
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==== gem5 educational hardware models
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TODO get some working!
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@@ -5963,8 +5967,6 @@ This protocol allows sharing a mountable filesystem between guest and host.
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With networking, it's boring, we can just use any of the old tools like sshfs and NFS.
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https://superuser.com/questions/628169/how-to-share-a-directory-with-the-host-without-networking-in-qemu
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One advantage of this method over NFS is that can run without `sudo` on host, or having to pass host credentials on guest for sshfs.
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TODO performance compared to NFS.
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@@ -6011,7 +6013,10 @@ security_model=mapped
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+
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writes from guest failed due to user mismatch problems: https://serverfault.com/questions/342801/read-write-access-for-passthrough-9p-filesystems-with-libvirt-qemu
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The feature is documented at: https://wiki.qemu.org/Documentation/9psetup
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Bibliography:
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* https://superuser.com/questions/628169/how-to-share-a-directory-with-the-host-without-networking-in-qemu
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* https://wiki.qemu.org/Documentation/9psetup
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==== 9P gem5
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@@ -6093,8 +6098,6 @@ We us this exact procedure to connect to <<gdbserver>>.
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===== ssh into guest
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https://unix.stackexchange.com/questions/124681/how-to-ssh-from-host-to-guest-using-qemu/307557#307557
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Not enabled by default due to the build / runtime overhead. To enable, build with:
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....
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@@ -6115,6 +6118,8 @@ And finally on host:
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ssh root@localhost -p 45456
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....
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Bibliography: https://unix.stackexchange.com/questions/124681/how-to-ssh-from-host-to-guest-using-qemu/307557#307557
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===== gem5 host to guest networking
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Could not do port forwarding from host to guest, and therefore could not use `gdbserver`: https://stackoverflow.com/questions/48941494/how-to-do-port-forwarding-from-guest-to-host-in-gem5
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@@ -6133,9 +6138,7 @@ gives:
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Could not open guest forwarding device 'guestfwd.tcp.45456'
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....
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Related:
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* https://serverfault.com/questions/769874/how-to-forward-a-port-from-guest-to-host-in-qemu-kvm
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Bibliography: https://serverfault.com/questions/769874/how-to-forward-a-port-from-guest-to-host-in-qemu-kvm
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==== Secondary disk
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@@ -6967,24 +6970,57 @@ Buildroot supports it, which makes everything just trivial:
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....
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./build -B 'BR2_PACKAGE_OPENBLAS=y' -k
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./run -F '/openblas.out'
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./run -F '/openblas.out; echo $?'
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....
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Outcome: the test passes:
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....
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0
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....
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Source: link:kernel_module/user/openblas.c[]
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The test performs a general matrix multiplication:
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....
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| 1.0 -3.0 | | 1.0 2.0 1.0 | | 0.5 0.5 0.5 | | 11.0 - 9.0 5.0 |
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1 * | 2.0 4.0 | * | -3.0 4.0 -1.0 | + 2 * | 0.5 0.5 0.5 | = | - 9.0 21.0 -1.0 |
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| 1.0 -1.0 | | 0.5 0.5 0.5 | | 5.0 - 1.0 3.0 |
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....
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This can be deduced from the Fortran interfaces at: `out/x86_64/buildroot/build/openblas-*/reference/dgemmf.f`, which we can map to our call as:
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....
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C := alpha*op( A )*op( B ) + beta*C,
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SUBROUTINE DGEMMF( TRANA, TRANB, M,N,K, ALPHA,A,LDA,B,LDB,BETA,C,LDC)
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cblas_dgemm( CblasColMajor, CblasNoTrans, CblasTrans,3,3,2 ,1, A,3, B,3, 2 ,C,3 );
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....
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===== Eigen
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Header only linear algebra library supported by Buildroot:
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Header only linear algebra library with a mainline Buildroot package:
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....
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./build -B 'BR2_PACKAGE_EIGEN=y' -k
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./run -F '/eigen_hello.out;/eigen_svd.out'
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....
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Source:
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Just create an array and print it:
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* link:kernel_module/user/eigen.cpp[]
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* link:kernel_module/user/eigen_svd.cpp[]
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....
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./run -F '/eigen.out'
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....
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Output:
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....
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3 -1
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2.5 1.5
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....
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Source: link:kernel_module/user/eigen.cpp[]
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This example just creates a matrix and prints it out.
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Tested on: link:http://github.com/cirosantilli/linux-kernel-module-cheat/commit/a4bdcf102c068762bb1ef26c591fcf71e5907525[a4bdcf102c068762bb1ef26c591fcf71e5907525]
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@@ -7658,7 +7694,7 @@ which gives pretty close results, and serve as a nice sanity check that the cycl
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It is also nice to see that `rdtsc` is a bit smaller than the `stats.txt` value, since the latter also includes the exec syscall for `m5`.
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See also:
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Bibliography:
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* https://en.wikipedia.org/wiki/Time_Stamp_Counter
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* https://stackoverflow.com/questions/9887839/clock-cycle-count-wth-gcc/9887979
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