Linux kernel patch and development source tree

It's a patch that undoes the earlier patch. It can be made with patch -R -pX bad.patch (where X is the number of directory levels to strip from the patch and bad.patch is the patch we want to undo) followed by a git commit

A "reversed patch" is when someone accidentally makes a patch with diff -u foo.c foo.c.orig (where foo.c is the newer file) instead of the correct diff -u foo.c.orig foo.c

The "reversed or previous applied patch" error indicates the patch has already been applied. I can not be more specific without knowing the contents of your kernelsuspend.patch file.

If you have the .git directory for the kernel source, you can look at the log for a single file with the git log command followed by the file name. e.g. git log fs/eventpoll.c or even git log -p fs/eventpoll.c.

Very roughly:

/dev contains device nodes, which in earlier Unix systems was the only way to interact with the kernel. There are two types of these, block devices and character devices. The corresponding API is geared to something that will allow block-based I/O (some kind of disk) or character based I/O (e.g. a serial port).

/sys (and /proc) were added later, possibly inspired by the Plan 9 OS. They provide complete directory subtrees, and the file entries in these subtrees contain text that describes the internal state of the kernel module when read, or, when written, set the internal state.

So a typical application would be:

You want to write a kernel driver for some kind of storage device? Use a /dev node to access the device itself, and /sys (or /proc) entries to fine-tune how the storage gets accessed.