-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
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
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
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:
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.
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