X-Git-Url: https://git.proxmox.com/?a=blobdiff_plain;f=CODING_STYLE;h=cb8edcbb3692c02ea9a369d6f3cbda3b91bf0596;hb=640dfb14db919462dedc1b4fa0feaaf99a0bff42;hp=1ab13b6861250e3fc812d678039ae99ca6b1845e;hpb=e68b98dc7237d76fdef5c5d403d0613b443102da;p=mirror_qemu.git

diff --git a/CODING_STYLE b/CODING_STYLE
index 1ab13b6861..cb8edcbb36 100644
--- a/CODING_STYLE
+++ b/CODING_STYLE
@@ -1,16 +1,19 @@
-Qemu Coding Style
+QEMU Coding Style
 =================
 
+Please use the script checkpatch.pl in the scripts directory to check
+patches before submitting.
+
 1. Whitespace
 
 Of course, the most important aspect in any coding style is whitespace.
 Crusty old coders who have trouble spotting the glasses on their noses
 can tell the difference between a tab and eight spaces from a distance
-of approximately fifteen parsecs.  Many a flamewar have been fought and
+of approximately fifteen parsecs.  Many a flamewar has been fought and
 lost on this issue.
 
 QEMU indents are four spaces.  Tabs are never used, except in Makefiles
-where they have been irreversibly coded into the syntax by some moron.
+where they have been irreversibly coded into the syntax.
 Spaces of course are superior to tabs because:
 
  - You have just one way to specify whitespace, not two.  Ambiguity breeds
@@ -26,9 +29,52 @@ Spaces of course are superior to tabs because:
 
 Do not leave whitespace dangling off the ends of lines.
 
+1.1 Multiline Indent
+
+There are several places where indent is necessary:
+
+ - if/else
+ - while/for
+ - function definition & call
+
+When breaking up a long line to fit within line width, we need a proper indent
+for the following lines.
+
+In case of if/else, while/for, align the secondary lines just after the
+opening parenthesis of the first.
+
+For example:
+
+    if (a == 1 &&
+        b == 2) {
+
+    while (a == 1 &&
+           b == 2) {
+
+In case of function, there are several variants:
+
+    * 4 spaces indent from the beginning
+    * align the secondary lines just after the opening parenthesis of the
+      first
+
+For example:
+
+    do_something(x, y,
+        z);
+
+    do_something(x, y,
+                 z);
+
+    do_something(x, do_another(y,
+                               z));
+
 2. Line width
 
-Lines are 80 characters; not longer.
+Lines should be 80 characters; try not to make them longer.
+
+Sometimes it is hard to do, especially when dealing with QEMU subsystems
+that use long function or symbol names.  Even in that case, do not make
+lines much longer than 80 characters.
 
 Rationale:
  - Some people like to tile their 24" screens with a 6x4 matrix of 80x24
@@ -36,18 +82,21 @@ Rationale:
    let them keep doing it.
  - Code and especially patches is much more readable if limited to a sane
    line length.  Eighty is traditional.
+ - The four-space indentation makes the most common excuse ("But look
+   at all that white space on the left!") moot.
  - It is the QEMU coding style.
 
 3. Naming
 
 Variables are lower_case_with_underscores; easy to type and read.  Structured
-type names are in CamelCase; harder to type but standing out.  Scalar type
+type names are in CamelCase; harder to type but standing out.  Enum type
+names and function type names should also be in CamelCase.  Scalar type
 names are lower_case_with_underscores_ending_with_a_t, like the POSIX
 uint64_t and family.  Note that this last convention contradicts POSIX
 and is therefore likely to be changed.
 
-Typedefs are used to eliminate the redundant 'struct' keyword.  It is the
-QEMU coding style.
+When wrapping standard library functions, use the prefix qemu_ to alert
+readers that they are seeing a wrapped version; otherwise avoid this prefix.
 
 4. Block structure
 
@@ -65,6 +114,10 @@ keyword.  Example:
         printf("a was something else entirely.\n");
     }
 
+Note that 'else if' is considered a single statement; otherwise a long if/
+else if/else if/.../else sequence would need an indent for every else
+statement.
+
 An exception is the opening brace for a function; for reasons of tradition
 and clarity it comes on a line by itself:
 
@@ -76,3 +129,88 @@ and clarity it comes on a line by itself:
 Rationale: a consistent (except for functions...) bracing style reduces
 ambiguity and avoids needless churn when lines are added or removed.
 Furthermore, it is the QEMU coding style.
+
+5. Declarations
+
+Mixed declarations (interleaving statements and declarations within
+blocks) are generally not allowed; declarations should be at the beginning
+of blocks.
+
+Every now and then, an exception is made for declarations inside a
+#ifdef or #ifndef block: if the code looks nicer, such declarations can
+be placed at the top of the block even if there are statements above.
+On the other hand, however, it's often best to move that #ifdef/#ifndef
+block to a separate function altogether.
+
+6. Conditional statements
+
+When comparing a variable for (in)equality with a constant, list the
+constant on the right, as in:
+
+    if (a == 1) {
+        /* Reads like: "If a equals 1" */
+        do_something();
+    }
+
+Rationale: Yoda conditions (as in 'if (1 == a)') are awkward to read.
+Besides, good compilers already warn users when '==' is mis-typed as '=',
+even when the constant is on the right.
+
+7. Comment style
+
+We use traditional C-style /* */ comments and avoid // comments.
+
+Rationale: The // form is valid in C99, so this is purely a matter of
+consistency of style. The checkpatch script will warn you about this.
+
+Multiline comment blocks should have a row of stars on the left,
+and the initial /* and terminating */ both on their own lines:
+    /*
+     * like
+     * this
+     */
+This is the same format required by the Linux kernel coding style.
+
+(Some of the existing comments in the codebase use the GNU Coding
+Standards form which does not have stars on the left, or other
+variations; avoid these when writing new comments, but don't worry
+about converting to the preferred form unless you're editing that
+comment anyway.)
+
+Rationale: Consistency, and ease of visually picking out a multiline
+comment from the surrounding code.
+
+8. trace-events style
+
+8.1 0x prefix
+
+In trace-events files, use a '0x' prefix to specify hex numbers, as in:
+
+some_trace(unsigned x, uint64_t y) "x 0x%x y 0x" PRIx64
+
+An exception is made for groups of numbers that are hexadecimal by
+convention and separated by the symbols '.', '/', ':', or ' ' (such as
+PCI bus id):
+
+another_trace(int cssid, int ssid, int dev_num) "bus id: %x.%x.%04x"
+
+However, you can use '0x' for such groups if you want. Anyway, be sure that
+it is obvious that numbers are in hex, ex.:
+
+data_dump(uint8_t c1, uint8_t c2, uint8_t c3) "bytes (in hex): %02x %02x %02x"
+
+Rationale: hex numbers are hard to read in logs when there is no 0x prefix,
+especially when (occasionally) the representation doesn't contain any letters
+and especially in one line with other decimal numbers. Number groups are allowed
+to not use '0x' because for some things notations like %x.%x.%x are used not
+only in Qemu. Also dumping raw data bytes with '0x' is less readable.
+
+8.2 '#' printf flag
+
+Do not use printf flag '#', like '%#x'.
+
+Rationale: there are two ways to add a '0x' prefix to printed number: '0x%...'
+and '%#...'. For consistency the only one way should be used. Arguments for
+'0x%' are:
+ - it is more popular
+ - '%#' omits the 0x for the value 0 which makes output inconsistent