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diff --git a/doc/hacker-guide/hacker-guide.tex b/doc/hacker-guide/hacker-guide.tex new file mode 100644 index 000000000..72c44df1a --- /dev/null +++ b/doc/hacker-guide/hacker-guide.tex @@ -0,0 +1,312 @@ +\documentclass{book}[12pt] +\usepackage{graphicx} +% \usepackage{fancyhdr} + +% \pagestyle{fancy} +\begin{document} + +% \headheight 117pt +% \rhead{\includegraphics{zr-logo.eps}} + +\author{Z Research} +\title{GlusterFS 1.3 Hacker's Guide} +\date{June 1, 2007} + +\maketitle +\frontmatter +\tableofcontents + +\mainmatter +\chapter{Introduction} + +\section{Coding guidelines} +GlusterFS uses GNU Arch for version control. To get the latest source do: +\begin{verbatim} + $ tla register-archive http://arch.sv.gnu.org/archives/gluster + $ tla -A gluster@sv.gnu.org get glusterfs--mainline--2.4 +\end{verbatim} +\noindent +GlusterFS follows the GNU coding +standards\footnote{http://www.gnu.org/prep/standards\_toc.html} for the +most part. + +\chapter{Major components} +\section{libglusterfs} +\texttt{libglusterfs} contains supporting code used by all the other components. +The important files here are: + +\texttt{dict.c}: This is an implementation of a serializable dictionary type. It is +used by the protocol code to send requests and replies. It is also used to pass options +to translators. + +\texttt{logging.c}: This is a thread-safe logging library. The log messages go to a +file (default \texttt{/usr/local/var/log/glusterfs/*}). + +\texttt{protocol.c}: This file implements the GlusterFS on-the-wire +protocol. The protocol itself is a simple ASCII protocol, designed to +be easy to parse and be human readable. + +A sample GlusterFS protocol block looks like this: +\begin{verbatim} + Block Start header + 0000000000000023 callid + 00000001 type + 00000016 op + xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx human-readable name + 00000000000000000000000000000ac3 block size + <...> block + Block End +\end{verbatim} + +\texttt{stack.h}: This file defines the \texttt{STACK\_WIND} and +\texttt{STACK\_UNWIND} macros which are used to implement the parallel +stack that is maintained for inter-xlator calls. See the \textsl{Taking control +of the stack} section below for more details. + +\texttt{spec.y}: This contains the Yacc grammar for the GlusterFS +specification file, and the parsing code. + + +Draw diagrams of trees +Two rules: +(1) directory structure is same +(2) file can exist only on one node + +\section{glusterfs-fuse} +\section{glusterfsd} +\section{transport} +\section{scheduler} +\section{xlator} + +\chapter{xlators} +\section{Taking control of the stack} +One can think of STACK\_WIND/UNWIND as a very specific RPC mechanism. + +% \includegraphics{stack.eps} + +\section{Overview of xlators} + +\flushleft{\LARGE\texttt{cluster/}} +\vskip 2ex +\flushleft{\Large\texttt{afr}} +\vskip 2ex +\flushleft{\Large\texttt{stripe}} +\vskip 2ex +\flushleft{\Large\texttt{unify}} + +\vskip 4ex +\flushleft{\LARGE\texttt{debug/}} +\vskip 2ex +\flushleft{\Large\texttt{trace}} +\vskip 2ex +The trace xlator simply logs all fops and mops, and passes them through to its child. + +\vskip 4ex +\flushleft{\LARGE\texttt{features/}} +\flushleft{\Large\texttt{posix-locks}} +\vskip 2ex +This xlator implements \textsc{posix} record locking semantics over +any kind of storage. + +\vskip 4ex +\flushleft{\LARGE\texttt{performance/}} + +\flushleft{\Large\texttt{io-threads}} +\vskip 2ex +\flushleft{\Large\texttt{read-ahead}} +\vskip 2ex +\flushleft{\Large\texttt{stat-prefetch}} +\vskip 2ex +\flushleft{\Large\texttt{write-behind}} +\vskip 2ex + +\vskip 4ex +\flushleft{\LARGE\texttt{protocol/}} +\vskip 2ex + +\flushleft{\Large\texttt{client}} +\vskip 2ex + +\flushleft{\Large\texttt{server}} +\vskip 2ex + +\vskip 4ex +\flushleft{\LARGE\texttt{storage/}} +\flushleft{\Large\texttt{posix}} +\vskip 2ex +The \texttt{posix} xlator is the one which actually makes calls to the +on-disk filesystem. Currently this is the only storage xlator available. However, +plans to develop other storage xlators, such as one for Amazon's S3 service, are +on the roadmap. + +\chapter{Writing a simple xlator} +\noindent +In this section we're going to write a rot13 xlator. ``Rot13'' is a +simple substitution cipher which obscures a text by replacing each +letter with the letter thirteen places down the alphabet. So `a' (0) +would become `n' (12), `b' would be 'm', and so on. Rot13 applied to +a piece of ciphertext yields the plaintext again, because rot13 is its +own inverse, since: + +\[ +x_c = x + 13\; (mod\; 26) +\] +\[ +x_c + 13\; (mod\; 26) = x + 13 + 13\; (mod\; 26) = x +\] + +First we include the requisite headers. + +\begin{verbatim} +#include <ctype.h> +#include <sys/uio.h> + +#include "glusterfs.h" +#include "xlator.h" +#include "logging.h" + +/* + * This is a rot13 ``encryption'' xlator. It rot13's data when + * writing to disk and rot13's it back when reading it. + * This xlator is meant as an example, not for production + * use ;) (hence no error-checking) + */ + +\end{verbatim} + +Then we write the rot13 function itself. For simplicity, we only transform lower case +letters. Any other byte is passed through as it is. + +\begin{verbatim} +/* We only handle lower case letters for simplicity */ +static void +rot13 (char *buf, int len) +{ + int i; + for (i = 0; i < len; i++) { + if (isalpha (buf[i])) + buf[i] = (buf[i] - 'a' + 13) % 26; + else if (buf[i] <= 26) + buf[i] = (buf[i] + 13) % 26 + 'a'; + } +} +\end{verbatim} + +Next comes a utility function whose purpose will be clear after looking at the code +below. + +\begin{verbatim} +static void +rot13_iovec (struct iovec *vector, int count) +{ + int i; + for (i = 0; i < count; i++) { + rot13 (vector[i].iov_base, vector[i].iov_len); + } +} +\end{verbatim} + +\begin{verbatim} +static int32_t +rot13_readv_cbk (call_frame_t *frame, + call_frame_t *prev_frame, + xlator_t *this, + int32_t op_ret, + int32_t op_errno, + struct iovec *vector, + int32_t count) +{ + rot13_iovec (vector, count); + + STACK_UNWIND (frame, op_ret, op_errno, vector, count); + return 0; +} + +static int32_t +rot13_readv (call_frame_t *frame, + xlator_t *this, + dict_t *ctx, + size_t size, + off_t offset) +{ + STACK_WIND (frame, + rot13_readv_cbk, + FIRST_CHILD (this), + FIRST_CHILD (this)->fops->readv, + ctx, size, offset); + return 0; +} + +static int32_t +rot13_writev_cbk (call_frame_t *frame, + call_frame_t *prev_frame, + xlator_t *this, + int32_t op_ret, + int32_t op_errno) +{ + STACK_UNWIND (frame, op_ret, op_errno); + return 0; +} + +static int32_t +rot13_writev (call_frame_t *frame, + xlator_t *this, + dict_t *ctx, + struct iovec *vector, + int32_t count, + off_t offset) +{ + rot13_iovec (vector, count); + + STACK_WIND (frame, + rot13_writev_cbk, + FIRST_CHILD (this), + FIRST_CHILD (this)->fops->writev, + ctx, vector, count, offset); + return 0; +} + +\end{verbatim} + +Every xlator must define two functions and two external symbols. The functions are +\texttt{init} and \texttt{fini}, and the symbols are \texttt{fops} and \texttt{mops}. +The \texttt{init} function is called when the xlator is loaded by GlusterFS, and +contains code for the xlator to initialize itself. Note that if an xlator is present +multiple times in the spec tree, the \texttt{init} function will be called each time +the xlator is loaded. + +\begin{verbatim} +int32_t +init (xlator_t *this) +{ + if (!this->children) { + gf_log ("rot13", GF_LOG_ERROR, + "FATAL: rot13 should have exactly one child"); + return -1; + } + + gf_log ("rot13", GF_LOG_DEBUG, "rot13 xlator loaded"); + return 0; +} +\end{verbatim} + +\begin{verbatim} + +void +fini (xlator_t *this) +{ + return; +} + +struct xlator_fops fops = { + .readv = rot13_readv, + .writev = rot13_writev +}; + +struct xlator_mops mops = { +}; + +\end{verbatim} + +\end{document} + |