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
------------------
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
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
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
with the new root (cd /newmount; mount --move . /; chroot .), attach
stdin/stdout/stderr to the new /dev/console, and exec the new init.
- Since this is a remarkably persnickity process (and involves deleting
+ Since this is a remarkably persnickety process (and involves deleting
commands before you can run them), the klibc package introduced a helper
program (utils/run_init.c) to do all this for you. Most other packages
(such as busybox) have named this command "switch_root".
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.
sleep(999999999);
}
EOF
- gcc -static hello2.c -o init
+ gcc -static hello.c -o init
echo init | cpio -o -H newc | gzip > test.cpio.gz
# Testing external initramfs using the initrd loading mechanism.
qemu -kernel /boot/vmlinuz -initrd test.cpio.gz /dev/zero
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,
projects / linux-2.6-omap-h63xx.git / blobdiff