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authorLubomir Rintel <lubo.rintel@gooddata.com>2013-07-31 15:37:33 +0200
committerVijay Bellur <vbellur@redhat.com>2013-08-04 07:36:13 -0700
commitd5a4e34f02415cfcc7637efaa1e135305a7da230 (patch)
treeca528f0a76c028b7103546ca6a98a7318a08679d
parentedb10e99d31516e00ef1822375375f676a12bf8a (diff)
doc: Convert the coding standards to markdown
Change-Id: I5f3bec7b86ce31beb7459a27dc0f4ba39c6d9610 Signed-off-by: Lubomir Rintel <lubo.rintel@gooddata.com> Reviewed-on: http://review.gluster.org/5479 Reviewed-by: Vijay Bellur <vbellur@redhat.com> Tested-by: Vijay Bellur <vbellur@redhat.com>
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+GlusterFS Coding Standards
+==========================
+
+Structure definitions should have a comment per member
+------------------------------------------------------
+
+Every member in a structure definition must have a comment about its
+purpose. The comment should be descriptive without being overly verbose.
+
+*Bad:*
+
+```
+gf_lock_t lock; /* lock */
+```
+
+*Good:*
+
+```
+DBTYPE access_mode; /* access mode for accessing
+ * the databases, can be
+ * DB_HASH, DB_BTREE
+ * (option access-mode <mode>)
+ */
+```
+
+Declare all variables at the beginning of the function
+------------------------------------------------------
+
+All local variables in a function must be declared immediately after the
+opening brace. This makes it easy to keep track of memory that needs to be freed
+during exit. It also helps debugging, since gdb cannot handle variables
+declared inside loops or other such blocks.
+
+Always initialize local variables
+---------------------------------
+
+Every local variable should be initialized to a sensible default value
+at the point of its declaration. All pointers should be initialized to NULL,
+and all integers should be zero or (if it makes sense) an error value.
+
+
+*Good:*
+
+```
+int ret = 0;
+char *databuf = NULL;
+int _fd = -1;
+```
+
+Initialization should always be done with a constant value
+----------------------------------------------------------
+
+Never use a non-constant expression as the initialization value for a variable.
+
+
+*Bad:*
+
+```
+pid_t pid = frame->root->pid;
+char *databuf = malloc (1024);
+```
+
+Validate all arguments to a function
+------------------------------------
+
+All pointer arguments to a function must be checked for `NULL`.
+A macro named `VALIDATE` (in `common-utils.h`)
+takes one argument, and if it is `NULL`, writes a log message and
+jumps to a label called `err` after setting op_ret and op_errno
+appropriately. It is recommended to use this template.
+
+
+*Good:*
+
+```
+VALIDATE(frame);
+VALIDATE(this);
+VALIDATE(inode);
+```
+
+Never rely on precedence of operators
+-------------------------------------
+
+Never write code that relies on the precedence of operators to execute
+correctly. Such code can be hard to read and someone else might not
+know the precedence of operators as accurately as you do.
+
+*Bad:*
+
+```
+if (op_ret == -1 && errno != ENOENT)
+```
+
+*Good:*
+
+```
+if ((op_ret == -1) && (errno != ENOENT))
+```
+
+Use exactly matching types
+--------------------------
+
+Use a variable of the exact type declared in the manual to hold the
+return value of a function. Do not use an ``equivalent'' type.
+
+
+*Bad:*
+
+```
+int len = strlen (path);
+```
+
+*Good:*
+
+```
+size_t len = strlen (path);
+```
+
+Never write code such as `foo->bar->baz`; check every pointer
+-------------------------------------------------------------
+
+Do not write code that blindly follows a chain of pointer
+references. Any pointer in the chain may be `NULL` and thus
+cause a crash. Verify that each pointer is non-null before following
+it.
+
+Check return value of all functions and system calls
+----------------------------------------------------
+
+The return value of all system calls and API functions must be checked
+for success or failure.
+
+*Bad:*
+
+```
+close (fd);
+```
+
+*Good:*
+
+```
+op_ret = close (_fd);
+if (op_ret == -1) {
+ gf_log (this->name, GF_LOG_ERROR,
+ "close on file %s failed (%s)", real_path,
+ strerror (errno));
+ op_errno = errno;
+ goto out;
+}
+```
+
+
+Gracefully handle failure of malloc
+-----------------------------------
+
+GlusterFS should never crash or exit due to lack of memory. If a
+memory allocation fails, the call should be unwound and an error
+returned to the user.
+
+*Use result args and reserve the return value to indicate success or failure:*
+
+The return value of every functions must indicate success or failure (unless
+it is impossible for the function to fail --- e.g., boolean functions). If
+the function needs to return additional data, it must be returned using a
+result (pointer) argument.
+
+*Bad:*
+
+```
+int32_t dict_get_int32 (dict_t *this, char *key);
+```
+
+*Good:*
+
+```
+int dict_get_int32 (dict_t *this, char *key, int32_t *val);
+```
+
+Always use the `n' versions of string functions
+-----------------------------------------------
+
+Unless impossible, use the length-limited versions of the string functions.
+
+*Bad:*
+
+```
+strcpy (entry_path, real_path);
+```
+
+*Good:*
+
+```
+strncpy (entry_path, real_path, entry_path_len);
+```
+
+No dead or commented code
+-------------------------
+
+There must be no dead code (code to which control can never be passed) or
+commented out code in the codebase.
+
+Only one unwind and return per function
+---------------------------------------
+
+There must be only one exit out of a function. `UNWIND` and return
+should happen at only point in the function.
+
+Function length or Keep functions small
+---------------------------------------
+
+We live in the UNIX-world where modules do one thing and do it well.
+This rule should apply to our functions also. If a function is very long, try splitting it
+into many little helper functions. The question is, in a coding
+spree, how do we know a function is long and unreadable. One rule of
+thumb given by Linus Torvalds is that, a function should be broken-up
+if you have 4 or more levels of indentation going on for more than 3-4
+lines.
+
+*Example for a helper function:*
+```
+static int
+same_owner (posix_lock_t *l1, posix_lock_t *l2)
+{
+ return ((l1->client_pid == l2->client_pid) &&
+ (l1->transport == l2->transport));
+}
+```
+
+Defining functions as static
+----------------------------
+
+Define internal functions as static only if you're
+very sure that there will not be a crash(..of any kind..) emanating in
+that function. If there is even a remote possibility, perhaps due to
+pointer derefering, etc, declare the function as non-static. This
+ensures that when a crash does happen, the function name shows up the
+in the back-trace generated by libc. However, doing so has potential
+for polluting the function namespace, so to avoid conflicts with other
+components in other parts, ensure that the function names are
+prepended with a prefix that identify the component to which it
+belongs. For eg. non-static functions in io-threads translator start
+with iot_.
+
+Ensure function calls wrap around after 80-columns
+--------------------------------------------------
+
+Place remaining arguments on the next line if needed.
+
+Functions arguments and function definition
+-------------------------------------------
+
+Place all the arguments of a function definition on the same line
+until the line goes beyond 80-cols. Arguments that extend beyind
+80-cols should be placed on the next line.
+
+Style issues
+------------
+
+### Brace placement
+
+Use K&R/Linux style of brace placement for blocks.
+
+*Good:*
+
+```
+int some_function (...)
+{
+ if (...) {
+ /* ... */
+ } else if (...) {
+ /* ... */
+ } else {
+ /* ... */
+ }
+
+ do {
+ /* ... */
+ } while (cond);
+}
+```
+
+### Indentation
+
+Use *eight* spaces for indenting blocks. Ensure that your
+file contains only spaces and not tab characters. You can do this
+in Emacs by selecting the entire file (`C-x h`) and
+running `M-x untabify`.
+
+To make Emacs indent lines automatically by eight spaces, add this
+line to your `.emacs`:
+
+```
+(add-hook 'c-mode-hook (lambda () (c-set-style "linux")))
+```
+
+### Comments
+
+Write a comment before every function describing its purpose (one-line),
+its arguments, and its return value. Mention whether it is an internal
+function or an exported function.
+
+Write a comment before every structure describing its purpose, and
+write comments about each of its members.
+
+Follow the style shown below for comments, since such comments
+can then be automatically extracted by doxygen to generate
+documentation.
+
+*Good:*
+
+```
+/**
+* hash_name -hash function for filenames
+* @par: parent inode number
+* @name: basename of inode
+* @mod: number of buckets in the hashtable
+*
+* @return: success: bucket number
+* failure: -1
+*
+* Not for external use.
+*/
+```
+
+### Indicating critical sections
+
+To clearly show regions of code which execute with locks held, use
+the following format:
+
+```
+pthread_mutex_lock (&mutex);
+{
+ /* code */
+}
+pthread_mutex_unlock (&mutex);
+```
+
+*A skeleton fop function:*
+
+This is the recommended template for any fop. In the beginning come
+the initializations. After that, the `success' control flow should be
+linear. Any error conditions should cause a `goto` to a single
+point, `out`. At that point, the code should detect the error
+that has occured and do appropriate cleanup.
+
+```
+int32_t
+sample_fop (call_frame_t *frame, xlator_t *this, ...)
+{
+ char * var1 = NULL;
+ int32_t op_ret = -1;
+ int32_t op_errno = 0;
+ DIR * dir = NULL;
+ struct posix_fd * pfd = NULL;
+
+ VALIDATE_OR_GOTO (frame, out);
+ VALIDATE_OR_GOTO (this, out);
+
+ /* other validations */
+
+ dir = opendir (...);
+
+ if (dir == NULL) {
+ op_errno = errno;
+ gf_log (this->name, GF_LOG_ERROR,
+ "opendir failed on %s (%s)", loc->path,
+ strerror (op_errno));
+ goto out;
+ }
+
+ /* another system call */
+ if (...) {
+ op_errno = ENOMEM;
+ gf_log (this->name, GF_LOG_ERROR,
+ "out of memory :(");
+ goto out;
+ }
+
+ /* ... */
+
+ out:
+ if (op_ret == -1) {
+
+ /* check for all the cleanup that needs to be
+ done */
+
+ if (dir) {
+ closedir (dir);
+ dir = NULL;
+ }
+
+ if (pfd) {
+ FREE (pfd->path);
+ FREE (pfd);
+ pfd = NULL;
+ }
+ }
+
+ STACK_UNWIND (frame, op_ret, op_errno, fd);
+ return 0;
+}
+```