diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/early-userspace/README | 6 | ||||
| -rw-r--r-- | Documentation/filesystems/ramfs-rootfs-initramfs.txt | 14 | ||||
| -rw-r--r-- | Documentation/initrd.txt | 12 | ||||
| -rw-r--r-- | Documentation/ramdisk.txt | 17 |
4 files changed, 27 insertions, 22 deletions
diff --git a/Documentation/early-userspace/README b/Documentation/early-userspace/README index cddbac456c29..766d320c8eb6 100644 --- a/Documentation/early-userspace/README +++ b/Documentation/early-userspace/README @@ -19,7 +19,7 @@ It consists of several major infrastructure components: - klibc, a userspace C library, currently packaged separately, that is optimized for correctness and small size. -The cpio file format used by initramfs is the "newc" (aka "cpio -c") +The cpio file format used by initramfs is the "newc" (aka "cpio -H newc") format, and is documented in the file "buffer-format.txt". There are two ways to add an early userspace image: specify an existing cpio archive to be used as the image or have the kernel build process build @@ -44,7 +44,7 @@ The image is specified as one or more sources in CONFIG_INITRAMFS_SOURCE. Sources can be either directories or files - cpio archives are *not* allowed when building from sources. -A source directory will have it and all of it's contents packaged. The +A source directory will have it and all of its contents packaged. The specified directory name will be mapped to '/'. When packaging a directory, limited user and group ID translation can be performed. INITRAMFS_ROOT_UID can be set to a user ID that needs to be mapped to @@ -144,7 +144,7 @@ c) using initramfs. The call to prepare_namespace() must be skipped. initrd format, an cpio archive. It must be called "/init". This binary is responsible to do all the things prepare_namespace() would do. - To remain backwards compatibility, the /init binary will only run if it + To maintain backwards compatibility, the /init binary will only run if it comes via an initramfs cpio archive. If this is not the case, init/main.c:init() will run prepare_namespace() to mount the final root and exec one of the predefined init binaries. diff --git a/Documentation/filesystems/ramfs-rootfs-initramfs.txt b/Documentation/filesystems/ramfs-rootfs-initramfs.txt index 25981e2e51be..339c6a4f220e 100644 --- a/Documentation/filesystems/ramfs-rootfs-initramfs.txt +++ b/Documentation/filesystems/ramfs-rootfs-initramfs.txt @@ -8,7 +8,7 @@ What is ramfs? Ramfs is a very simple filesystem that exports Linux's disk caching mechanisms (the page cache and dentry cache) as a dynamically resizable -ram-based filesystem. +RAM-based filesystem. Normally all files are cached in memory by Linux. Pages of data read from backing store (usually the block device the filesystem is mounted on) are kept @@ -34,7 +34,7 @@ ramfs and ramdisk: ------------------ The older "ram disk" mechanism created a synthetic block device out of -an area of ram and used it as backing store for a filesystem. This block +an area of RAM and used it as backing store for a filesystem. This block device was of fixed size, so the filesystem mounted on it was of fixed size. Using a ram disk also required unnecessarily copying memory from the fake block device into the page cache (and copying changes back out), as well @@ -46,8 +46,8 @@ unnecessary work for the CPU, and pollutes the CPU caches. (There are tricks to avoid this copying by playing with the page tables, but they're unpleasantly complicated and turn out to be about as expensive as the copying anyway.) More to the point, all the work ramfs is doing has to happen _anyway_, -since all file access goes through the page and dentry caches. The ram -disk is simply unnecessary, ramfs is internally much simpler. +since all file access goes through the page and dentry caches. The RAM +disk is simply unnecessary; ramfs is internally much simpler. Another reason ramdisks are semi-obsolete is that the introduction of loopback devices offered a more flexible and convenient way to create @@ -103,7 +103,7 @@ All this differs from the old initrd in several ways: initramfs archive is a gzipped cpio archive (like tar only simpler, see cpio(1) and Documentation/early-userspace/buffer-format.txt). The kernel's cpio extraction code is not only extremely small, it's also - __init data that can be discarded during the boot process. + __init text and data that can be discarded during the boot process. - The program run by the old initrd (which was called /initrd, not /init) did some setup and then returned to the kernel, while the init program from @@ -220,7 +220,7 @@ device) but the separate packaging of initrd (which is nice if you have non-GPL code you'd like to run from initramfs, without conflating it with the GPL licensed Linux kernel binary). -It can also be used to supplement the kernel's built-in initamfs image. The +It can also be used to supplement the kernel's built-in initramfs image. The files in the external archive will overwrite any conflicting files in the built-in initramfs archive. Some distributors also prefer to customize a single kernel image with task-specific initramfs images, without recompiling. @@ -339,7 +339,7 @@ smooth transition and allowing early boot functionality to gradually move to The move to early userspace is necessary because finding and mounting the real root device is complex. Root partitions can span multiple devices (raid or separate journal). They can be out on the network (requiring dhcp, setting a -specific mac address, logging into a server, etc). They can live on removable +specific MAC address, logging into a server, etc). They can live on removable media, with dynamically allocated major/minor numbers and persistent naming issues requiring a full udev implementation to sort out. They can be compressed, encrypted, copy-on-write, loopback mounted, strangely partitioned, diff --git a/Documentation/initrd.txt b/Documentation/initrd.txt index d3dc505104da..74f68b35f7c1 100644 --- a/Documentation/initrd.txt +++ b/Documentation/initrd.txt @@ -80,8 +80,8 @@ Compressed cpio images ---------------------- Recent kernels have support for populating a ramdisk from a compressed cpio -archive, on such systems, the creation of a ramdisk image doesn't need to -involve special block devices or loopbacks, you merely create a directory on +archive. On such systems, the creation of a ramdisk image doesn't need to +involve special block devices or loopbacks; you merely create a directory on disk with the desired initrd content, cd to that directory, and run (as an example): @@ -293,7 +293,7 @@ information as small as possible. In this case, a common initrd could be generated with all the necessary modules. Then, only /sbin/init or a file read by it would have to be different. -A third scenario are more convenient recovery disks, because information +A third scenario is more convenient recovery disks, because information like the location of the root FS partition doesn't have to be provided at boot time, but the system loaded from initrd can invoke a user-friendly dialog and it can also perform some sanity checks (or even some form of @@ -339,8 +339,8 @@ the new, supported mechanism is called "pivot_root". Mixed change_root and pivot_root mechanism ------------------------------------------ -In case you did not want to use root=/dev/ram0 to trig the pivot_root mechanism, -you may create both /linuxrc and /sbin/init in your initrd image. +In case you did not want to use root=/dev/ram0 to trigger the pivot_root +mechanism, you may create both /linuxrc and /sbin/init in your initrd image. /linuxrc would contain only the following: @@ -350,7 +350,7 @@ echo 0x0100 >/proc/sys/kernel/real-root-dev umount -n /proc Once linuxrc exited, the kernel would mount again your initrd as root, -this time executing /sbin/init. Again, it would be duty of this init +this time executing /sbin/init. Again, it would be the duty of this init to build the right environment (maybe using the root= device passed on the cmdline) before the final execution of the real /sbin/init. diff --git a/Documentation/ramdisk.txt b/Documentation/ramdisk.txt index 52f75b7d51c2..33e987df071e 100644 --- a/Documentation/ramdisk.txt +++ b/Documentation/ramdisk.txt @@ -22,16 +22,21 @@ The RAM disk dynamically grows as more space is required. It does this by using RAM from the buffer cache. The driver marks the buffers it is using as dirty so that the VM subsystem does not try to reclaim them later. -Also, the RAM disk supports up to 16 RAM disks out of the box, and can -be reconfigured to support up to 255 RAM disks - change "#define NUM_RAMDISKS" -in drivers/block/rd.c. To use RAM disk support with your system, run -'./MAKEDEV ram' from the /dev directory. RAM disks are all major number 1, and -start with minor number 0 for /dev/ram0, etc. If used, modern kernels use -/dev/ram0 for an initrd. +The RAM disk supports up to 16 RAM disks by default, and can be reconfigured +to support an unlimited number of RAM disks (at your own risk). Just change +the configuration symbol BLK_DEV_RAM_COUNT in the Block drivers config menu +and (re)build the kernel. + +To use RAM disk support with your system, run './MAKEDEV ram' from the /dev +directory. RAM disks are all major number 1, and start with minor number 0 +for /dev/ram0, etc. If used, modern kernels use /dev/ram0 for an initrd. The old "ramdisk=<ram_size>" has been changed to "ramdisk_size=<ram_size>" to make it clearer. The original "ramdisk=<ram_size>" has been kept around for compatibility reasons, but it may be removed in the future. +There are also config symbols (in the Block drivers config menu) for these +variables: BLK_DEV_RAM_SIZE defaults to 4096 and BLK_DEV_RAM_BLOCKSIZE +defaults to 1024. The new RAM disk also has the ability to load compressed RAM disk images, allowing one to squeeze more programs onto an average installation or |