linux.tex

nandflash文件系统源代码

Debugging efsl on embedded devices is a rather hard job, because
you can't just printf debug strings or watch memory maps easily. 
Because of that, core development has been performed under the 
Linux operating system. Under Linux, efsl can be compiled as 
library and used as a userspace filesystem handler. On Unix-
style operating system (like Linux), all devices (usb stick, disc, \ldots)
can be seen as a file, and as such been opened by efsl.\newline
\newline
In the following section, we will explain how to get started using
efsl as userspace filesystem handler. However, please note that the main
focus for efsl is to support embedded systems, which usually don't even
have 1\% of the memory you have on a PC. Accessing files on a FAT-filesystem
with efsl will be much slower than when accessing these files with the Linux
FAT kernel modules.
\subsubsection{Download \& Compile}
Let's get started:
\begin{enumerate}
	\item{Get the latest release of efsl on http://www.sf.net/projects/efsl/ 
		and put it in your homedir}
	\item{Unpack the library (tar xvfj efsl-version.tar.bz2)}
	\item{Get inside the directory (cd $\sim$/efsl)}
	\item{Create a symlink from \filename{Makefile-LINUX} to \filename{Makefile} 
		(ln -s Makefile-LINUX Makefile)}
	\item{Copy \filename{conf/config-sample-linux.h} to \filename{conf/config.h}
		(cp conf/config-sample-linux.h conf/config.h)}
	\item{Compile the library (make lib)}
	\item{Find the compiled filesystem library (libefsl.a) in the current 
		directory}
\end{enumerate}
If you got any errors with the steps above, please check that that you have
the following packages installed: tar, gcc, libgcc, binutils \& make.
\subsubsection{Example}
Since efsl itself is only a library, it's not supposed to do anything
out of the box, than just compile. To get started, we'll show here a small
example program that opens a file on a disc/usb-stick/floppy that contains
a FAT-filesystem and prints it's content to stdout.\newline
\newline
First, create a new directory in which you put the compiled efsl-library
(\filename{libefsl.a}) and create a new file called \filename{linuxtest.c} containing:
\lstset{numbers=left, stepnumber=1, numberstyle=\small, numbersep=5pt, tabsize=4}
\begin{lstlisting}
	#include <stdio.h>
	#include <efs.h>
 
	int main(void)
	{
		EmbeddedFileSystem efs;
		EmbeddedFile file;
		unsigned short i,e;
		char buf[512];
	
		if(efs_init(&efs,"/dev/sda")!=0){
			printf("Could not open filesystem.\n");
			return(-1);
		}
	
		if(file_fopen(&file,&efs.myFs,"group",'r')!=0){
			printf("Could not open file.\n");
			return(-2);
		}

		while(e=file_read(&file,512,buf)){
			for(i=0;i<e;i++)
			printf("\%c",buf[i]);
		}
	
		return(0);
	}
\end{lstlisting}
$ $\newline
Some extra information on the code above:
\begin{itemize}
	\item{Line 1-2: The header files for stdio (used for printf) and efsl 
		are included. When using the basic efsl functions, \filename{efs.h} is
		the only header file of the efsl library that needs to be included.}
	\item{Line 6: The object efs is created, this object will contain 
		information about the hardware layer, the partition table and
		the disc.}
	\item{Line 7: The object file is created, this object will contain
		information about the file that we will open on the efs-object.}
	\item{Line 9: A buffer of 512 bytes is allocated. This buffer will
	 	be filled by fread with data.}
	\item{Line 11-14: Call of \code{efs\_init}, which will initialize the efs-object.
		To this function we pass:
		\begin{enumerate}
			\item{A pointer to the efs-object.}
			\item{A pointer to the file that contains the partition table /
				file system (in this example, we select a device as file).}
		\end{enumerate}
		If this function returns 0, it means that a valid fat partition is
		found on the device given. 
		If no valid fat-filesystem is found, or the file does not exist, the 
		function returns a negative value. In this example we then print an
		error message and quit.}
	\item{Line 16-19: Call of \code{file\_fopen()}, which will initialize the 
		file-object. To this function we pass:
		\begin{enumerate}
			\item{A pointer to the file-object.}
			\item{A pointer to the filesystem-object.} 
			\item{A pointer to the filename.}
			\item{A char containing the the mode (read, write, append).}
		\end{enumerate}
		If this function returns 0, it means the file has successfully been
		opened for reading / writing / appending.
		If the file could not be opened, a negative value is returned.
	}
	\item{Line 21-24: Call of \code{file\_read()}, which will read a given value of
		bytes (in this example 512) from a file and put it's content into
		the buffer passed (in this example called buf). This function returns
		the amount of bytes read, so the while-loop will be executed as long
		as there are bytes left in the file. The code inside the while-loop
		will print all characters in the buffer.}
\end{itemize}
\subsubsection{Testing}
So now let's test the program:
\begin{enumerate}
	\item{Compile the program 
		(gcc -I/home/user/efsl/inc/ -I/home/user/efsl/conf -o linuxtest 
		linuxtest.c -L./ -lefsl).}
	\item{Insert a usb-disc, floppy, mp3-stick, \ldots with a valid 
		fat-filesystem on it.}
	\item{Mount the device, copy the file /etc/group on it's root dir \& umount
		it.}
	\item{Check that you have permission to access the device
		(chown username /dev/sda*)}
	\item{Run the program (./linuxtest)}
\end{enumerate}