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author | Linus Torvalds <torvalds@linux-foundation.org> | 2020-10-12 16:21:29 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2020-10-12 16:21:29 -0700 |
commit | 50d228345a03c882dfe11928ab41b42458b3f922 (patch) | |
tree | 31a8894ec4986f02802be9daac29c36839df084e /Documentation/admin-guide/blockdev/ramdisk.rst | |
parent | Merge tag 'ia64_for_5.10' of git://git.kernel.org/pub/scm/linux/kernel/git/aegl/linux (diff) | |
parent | gpiolib: Update indentation in driver.rst for code excerpts (diff) | |
download | linux-dev-50d228345a03c882dfe11928ab41b42458b3f922.tar.xz linux-dev-50d228345a03c882dfe11928ab41b42458b3f922.zip |
Merge tag 'docs-5.10' of git://git.lwn.net/linux
Pull documentation updates from Jonathan Corbet:
"As hoped, things calmed down for docs this cycle; fewer changes and
almost no conflicts at all. This includes:
- A reworked and expanded user-mode Linux document
- Some simplifications and improvements for submitting-patches.rst
- An emergency fix for (some) problems with Sphinx 3.x
- Some welcome automarkup improvements to automatically generate
cross-references to struct definitions and other documents
- The usual collection of translation updates, typo fixes, etc"
* tag 'docs-5.10' of git://git.lwn.net/linux: (81 commits)
gpiolib: Update indentation in driver.rst for code excerpts
Documentation/admin-guide: tainted-kernels: Fix typo occured
Documentation: better locations for sysfs-pci, sysfs-tagging
docs: programming-languages: refresh blurb on clang support
Documentation: kvm: fix a typo
Documentation: Chinese translation of Documentation/arm64/amu.rst
doc: zh_CN: index files in arm64 subdirectory
mailmap: add entry for <mstarovoitov@marvell.com>
doc: seq_file: clarify role of *pos in ->next()
docs: trace: ring-buffer-design.rst: use the new SPDX tag
Documentation: kernel-parameters: clarify "module." parameters
Fix references to nommu-mmap.rst
docs: rewrite admin-guide/sysctl/abi.rst
docs: fb: Remove vesafb scrollback boot option
docs: fb: Remove sstfb scrollback boot option
docs: fb: Remove matroxfb scrollback boot option
docs: fb: Remove framebuffer scrollback boot option
docs: replace the old User Mode Linux HowTo with a new one
Documentation/admin-guide: blockdev/ramdisk: remove use of "rdev"
Documentation/admin-guide: README & svga: remove use of "rdev"
...
Diffstat (limited to 'Documentation/admin-guide/blockdev/ramdisk.rst')
-rw-r--r-- | Documentation/admin-guide/blockdev/ramdisk.rst | 66 |
1 files changed, 21 insertions, 45 deletions
diff --git a/Documentation/admin-guide/blockdev/ramdisk.rst b/Documentation/admin-guide/blockdev/ramdisk.rst index b7c2268f8dec..9ce6101e8dd9 100644 --- a/Documentation/admin-guide/blockdev/ramdisk.rst +++ b/Documentation/admin-guide/blockdev/ramdisk.rst @@ -6,7 +6,7 @@ Using the RAM disk block device with Linux 1) Overview 2) Kernel Command Line Parameters - 3) Using "rdev -r" + 3) Using "rdev" 4) An Example of Creating a Compressed RAM Disk @@ -59,51 +59,27 @@ default is 4096 (4 MB). rd_size See ramdisk_size. -3) Using "rdev -r" ------------------- +3) Using "rdev" +--------------- -The usage of the word (two bytes) that "rdev -r" sets in the kernel image is -as follows. The low 11 bits (0 -> 10) specify an offset (in 1 k blocks) of up -to 2 MB (2^11) of where to find the RAM disk (this used to be the size). Bit -14 indicates that a RAM disk is to be loaded, and bit 15 indicates whether a -prompt/wait sequence is to be given before trying to read the RAM disk. Since -the RAM disk dynamically grows as data is being written into it, a size field -is not required. Bits 11 to 13 are not currently used and may as well be zero. -These numbers are no magical secrets, as seen below:: +"rdev" is an obsolete, deprecated, antiquated utility that could be used +to set the boot device in a Linux kernel image. - ./arch/x86/kernel/setup.c:#define RAMDISK_IMAGE_START_MASK 0x07FF - ./arch/x86/kernel/setup.c:#define RAMDISK_PROMPT_FLAG 0x8000 - ./arch/x86/kernel/setup.c:#define RAMDISK_LOAD_FLAG 0x4000 +Instead of using rdev, just place the boot device information on the +kernel command line and pass it to the kernel from the bootloader. -Consider a typical two floppy disk setup, where you will have the -kernel on disk one, and have already put a RAM disk image onto disk #2. +You can also pass arguments to the kernel by setting FDARGS in +arch/x86/boot/Makefile and specify in initrd image by setting FDINITRD in +arch/x86/boot/Makefile. -Hence you want to set bits 0 to 13 as 0, meaning that your RAM disk -starts at an offset of 0 kB from the beginning of the floppy. -The command line equivalent is: "ramdisk_start=0" +Some of the kernel command line boot options that may apply here are:: -You want bit 14 as one, indicating that a RAM disk is to be loaded. -The command line equivalent is: "load_ramdisk=1" - -You want bit 15 as one, indicating that you want a prompt/keypress -sequence so that you have a chance to switch floppy disks. -The command line equivalent is: "prompt_ramdisk=1" - -Putting that together gives 2^15 + 2^14 + 0 = 49152 for an rdev word. -So to create disk one of the set, you would do:: - - /usr/src/linux# cat arch/x86/boot/zImage > /dev/fd0 - /usr/src/linux# rdev /dev/fd0 /dev/fd0 - /usr/src/linux# rdev -r /dev/fd0 49152 + ramdisk_start=N + ramdisk_size=M If you make a boot disk that has LILO, then for the above, you would use:: - append = "ramdisk_start=0 load_ramdisk=1 prompt_ramdisk=1" - -Since the default start = 0 and the default prompt = 1, you could use:: - - append = "load_ramdisk=1" - + append = "ramdisk_start=N ramdisk_size=M" 4) An Example of Creating a Compressed RAM Disk ----------------------------------------------- @@ -151,12 +127,9 @@ f) Put the RAM disk image onto the floppy, after the kernel. Use an offset dd if=/tmp/ram_image.gz of=/dev/fd0 bs=1k seek=400 -g) Use "rdev" to set the boot device, RAM disk offset, prompt flag, etc. - For prompt_ramdisk=1, load_ramdisk=1, ramdisk_start=400, one would - have 2^15 + 2^14 + 400 = 49552:: - - rdev /dev/fd0 /dev/fd0 - rdev -r /dev/fd0 49552 +g) Make sure that you have already specified the boot information in + FDARGS and FDINITRD or that you use a bootloader to pass kernel + command line boot options to the kernel. That is it. You now have your boot/root compressed RAM disk floppy. Some users may wish to combine steps (d) and (f) by using a pipe. @@ -167,11 +140,14 @@ users may wish to combine steps (d) and (f) by using a pipe. Changelog: ---------- +SEPT-2020 : + + Removed usage of "rdev" + 10-22-04 : Updated to reflect changes in command line options, remove obsolete references, general cleanup. James Nelson (james4765@gmail.com) - 12-95 : Original Document |