Re: [Qemu-devel] [PATCH v2 2/4] docs: merge HACKING.rst contents into CODING_STYLE.rst

[Alex Bennée]

Daniel P. Berrangé <address@hidden> writes:

> The split of information between the two docs is rather arbitary and
> unclear. It is simpler for contributors if all the information is in
> one file.
>
> Signed-off-by: Daniel P. Berrangé <address@hidden>

Reviewed-by: Alex Bennée <address@hidden>

> ---
>  CODING_STYLE.rst | 296 ++++++++++++++++++++++++++++++++++++++++++++++
>  HACKING.rst      | 300 -----------------------------------------------
>  README.rst       |   2 +-
>  3 files changed, 297 insertions(+), 301 deletions(-)
>  delete mode 100644 HACKING.rst
>
> diff --git a/CODING_STYLE.rst b/CODING_STYLE.rst
> index 713357cb80..4501d87352 100644
> --- a/CODING_STYLE.rst
> +++ b/CODING_STYLE.rst
> @@ -205,6 +205,302 @@ comment anyway.)
>  Rationale: Consistency, and ease of visually picking out a multiline
>  comment from the surrounding code.
>
> +Preprocessor
> +============
> +
> +Variadic macros
> +---------------
> +
> +For variadic macros, stick with this C99-like syntax:
> +
> +.. code-block:: c
> +
> +    #define DPRINTF(fmt, ...)                                       \
> +        do { printf("IRQ: " fmt, ## __VA_ARGS__); } while (0)
> +
> +Include directives
> +------------------
> +
> +Order include directives as follows:
> +
> +.. code-block:: c
> +
> +    #include "qemu/osdep.h"  /* Always first... */
> +    #include <...>           /* then system headers... */
> +    #include "..."           /* and finally QEMU headers. */
> +
> +The "qemu/osdep.h" header contains preprocessor macros that affect the 
> behavior
> +of core system headers like <stdint.h>.  It must be the first include so that
> +core system headers included by external libraries get the preprocessor 
> macros
> +that QEMU depends on.
> +
> +Do not include "qemu/osdep.h" from header files since the .c file will have
> +already included it.
> +
> +C types
> +=======
> +
> +It should be common sense to use the right type, but we have collected
> +a few useful guidelines here.
> +
> +Scalars
> +-------
> +
> +If you're using "int" or "long", odds are good that there's a better type.
> +If a variable is counting something, it should be declared with an
> +unsigned type.
> +
> +If it's host memory-size related, size_t should be a good choice (use
> +ssize_t only if required). Guest RAM memory offsets must use ram_addr_t,
> +but only for RAM, it may not cover whole guest address space.
> +
> +If it's file-size related, use off_t.
> +If it's file-offset related (i.e., signed), use off_t.
> +If it's just counting small numbers use "unsigned int";
> +(on all but oddball embedded systems, you can assume that that
> +type is at least four bytes wide).
> +
> +In the event that you require a specific width, use a standard type
> +like int32_t, uint32_t, uint64_t, etc.  The specific types are
> +mandatory for VMState fields.
> +
> +Don't use Linux kernel internal types like u32, __u32 or __le32.
> +
> +Use hwaddr for guest physical addresses except pcibus_t
> +for PCI addresses.  In addition, ram_addr_t is a QEMU internal address
> +space that maps guest RAM physical addresses into an intermediate
> +address space that can map to host virtual address spaces.  Generally
> +speaking, the size of guest memory can always fit into ram_addr_t but
> +it would not be correct to store an actual guest physical address in a
> +ram_addr_t.
> +
> +For CPU virtual addresses there are several possible types.
> +vaddr is the best type to use to hold a CPU virtual address in
> +target-independent code. It is guaranteed to be large enough to hold a
> +virtual address for any target, and it does not change size from target
> +to target. It is always unsigned.
> +target_ulong is a type the size of a virtual address on the CPU; this means
> +it may be 32 or 64 bits depending on which target is being built. It should
> +therefore be used only in target-specific code, and in some
> +performance-critical built-per-target core code such as the TLB code.
> +There is also a signed version, target_long.
> +abi_ulong is for the ``*``-user targets, and represents a type the size of
> +'void ``*``' in that target's ABI. (This may not be the same as the size of a
> +full CPU virtual address in the case of target ABIs which use 32 bit pointers
> +on 64 bit CPUs, like sparc32plus.) Definitions of structures that must match
> +the target's ABI must use this type for anything that on the target is 
> defined
> +to be an 'unsigned long' or a pointer type.
> +There is also a signed version, abi_long.
> +
> +Of course, take all of the above with a grain of salt.  If you're about
> +to use some system interface that requires a type like size_t, pid_t or
> +off_t, use matching types for any corresponding variables.
> +
> +Also, if you try to use e.g., "unsigned int" as a type, and that
> +conflicts with the signedness of a related variable, sometimes
> +it's best just to use the *wrong* type, if "pulling the thread"
> +and fixing all related variables would be too invasive.
> +
> +Finally, while using descriptive types is important, be careful not to
> +go overboard.  If whatever you're doing causes warnings, or requires
> +casts, then reconsider or ask for help.
> +
> +Pointers
> +--------
> +
> +Ensure that all of your pointers are "const-correct".
> +Unless a pointer is used to modify the pointed-to storage,
> +give it the "const" attribute.  That way, the reader knows
> +up-front that this is a read-only pointer.  Perhaps more
> +importantly, if we're diligent about this, when you see a non-const
> +pointer, you're guaranteed that it is used to modify the storage
> +it points to, or it is aliased to another pointer that is.
> +
> +Typedefs
> +--------
> +
> +Typedefs are used to eliminate the redundant 'struct' keyword, since type
> +names have a different style than other identifiers ("CamelCase" versus
> +"snake_case").  Each named struct type should have a CamelCase name and a
> +corresponding typedef.
> +
> +Since certain C compilers choke on duplicated typedefs, you should avoid
> +them and declare a typedef only in one header file.  For common types,
> +you can use "include/qemu/typedefs.h" for example.  However, as a matter
> +of convenience it is also perfectly fine to use forward struct
> +definitions instead of typedefs in headers and function prototypes; this
> +avoids problems with duplicated typedefs and reduces the need to include
> +headers from other headers.
> +
> +Reserved namespaces in C and POSIX
> +----------------------------------
> +
> +Underscore capital, double underscore, and underscore 't' suffixes should be
> +avoided.
> +
> +Low level memory management
> +===========================
> +
> +Use of the malloc/free/realloc/calloc/valloc/memalign/posix_memalign
> +APIs is not allowed in the QEMU codebase. Instead of these routines,
> +use the GLib memory allocation routines g_malloc/g_malloc0/g_new/
> +g_new0/g_realloc/g_free or QEMU's qemu_memalign/qemu_blockalign/qemu_vfree
> +APIs.
> +
> +Please note that g_malloc will exit on allocation failure, so there
> +is no need to test for failure (as you would have to with malloc).
> +Calling g_malloc with a zero size is valid and will return NULL.
> +
> +Prefer g_new(T, n) instead of g_malloc(sizeof(T) ``*`` n) for the following
> +reasons:
> +
> +* It catches multiplication overflowing size_t;
> +* It returns T ``*`` instead of void ``*``, letting compiler catch more type 
> errors.
> +
> +Declarations like
> +
> +.. code-block:: c
> +
> +    T *v = g_malloc(sizeof(*v))
> +
> +are acceptable, though.
> +
> +Memory allocated by qemu_memalign or qemu_blockalign must be freed with
> +qemu_vfree, since breaking this will cause problems on Win32.
> +
> +String manipulation
> +===================
> +
> +Do not use the strncpy function.  As mentioned in the man page, it does *not*
> +guarantee a NULL-terminated buffer, which makes it extremely dangerous to 
> use.
> +It also zeros trailing destination bytes out to the specified length.  
> Instead,
> +use this similar function when possible, but note its different signature:
> +
> +.. code-block:: c
> +
> +    void pstrcpy(char *dest, int dest_buf_size, const char *src)
> +
> +Don't use strcat because it can't check for buffer overflows, but:
> +
> +.. code-block:: c
> +
> +    char *pstrcat(char *buf, int buf_size, const char *s)
> +
> +The same limitation exists with sprintf and vsprintf, so use snprintf and
> +vsnprintf.
> +
> +QEMU provides other useful string functions:
> +
> +.. code-block:: c
> +
> +    int strstart(const char *str, const char *val, const char **ptr)
> +    int stristart(const char *str, const char *val, const char **ptr)
> +    int qemu_strnlen(const char *s, int max_len)
> +
> +There are also replacement character processing macros for isxyz and toxyz,
> +so instead of e.g. isalnum you should use qemu_isalnum.
> +
> +Because of the memory management rules, you must use g_strdup/g_strndup
> +instead of plain strdup/strndup.
> +
> +Printf-style functions
> +======================
> +
> +Whenever you add a new printf-style function, i.e., one with a format
> +string argument and following "..." in its prototype, be sure to use
> +gcc's printf attribute directive in the prototype.
> +
> +This makes it so gcc's -Wformat and -Wformat-security options can do
> +their jobs and cross-check format strings with the number and types
> +of arguments.
> +
> +C standard, implementation defined and undefined behaviors
> +==========================================================
> +
> +C code in QEMU should be written to the C99 language specification. A copy
> +of the final version of the C99 standard with corrigenda TC1, TC2, and TC3
> +included, formatted as a draft, can be downloaded from:
> +
> +    `<http://www.open-std.org/jtc1/sc22/WG14/www/docs/n1256.pdf>`_
> +
> +The C language specification defines regions of undefined behavior and
> +implementation defined behavior (to give compiler authors enough leeway to
> +produce better code).  In general, code in QEMU should follow the language
> +specification and avoid both undefined and implementation defined
> +constructs. ("It works fine on the gcc I tested it with" is not a valid
> +argument...) However there are a few areas where we allow ourselves to
> +assume certain behaviors because in practice all the platforms we care about
> +behave in the same way and writing strictly conformant code would be
> +painful. These are:
> +
> +* you may assume that integers are 2s complement representation
> +* you may assume that right shift of a signed integer duplicates
> +  the sign bit (ie it is an arithmetic shift, not a logical shift)
> +
> +In addition, QEMU assumes that the compiler does not use the latitude
> +given in C99 and C11 to treat aspects of signed '<<' as undefined, as
> +documented in the GNU Compiler Collection manual starting at version 4.0.
> +
> +Error handling and reporting
> +============================
> +
> +Reporting errors to the human user
> +----------------------------------
> +
> +Do not use printf(), fprintf() or monitor_printf().  Instead, use
> +error_report() or error_vreport() from error-report.h.  This ensures the
> +error is reported in the right place (current monitor or stderr), and in
> +a uniform format.
> +
> +Use error_printf() & friends to print additional information.
> +
> +error_report() prints the current location.  In certain common cases
> +like command line parsing, the current location is tracked
> +automatically.  To manipulate it manually, use the loc_``*``() from
> +error-report.h.
> +
> +Propagating errors
> +------------------
> +
> +An error can't always be reported to the user right where it's detected,
> +but often needs to be propagated up the call chain to a place that can
> +handle it.  This can be done in various ways.
> +
> +The most flexible one is Error objects.  See error.h for usage
> +information.
> +
> +Use the simplest suitable method to communicate success / failure to
> +callers.  Stick to common methods: non-negative on success / -1 on
> +error, non-negative / -errno, non-null / null, or Error objects.
> +
> +Example: when a function returns a non-null pointer on success, and it
> +can fail only in one way (as far as the caller is concerned), returning
> +null on failure is just fine, and certainly simpler and a lot easier on
> +the eyes than propagating an Error object through an Error ``*````*`` 
> parameter.
> +
> +Example: when a function's callers need to report details on failure
> +only the function really knows, use Error ``*````*``, and set suitable 
> errors.
> +
> +Do not report an error to the user when you're also returning an error
> +for somebody else to handle.  Leave the reporting to the place that
> +consumes the error returned.
> +
> +Handling errors
> +---------------
> +
> +Calling exit() is fine when handling configuration errors during
> +startup.  It's problematic during normal operation.  In particular,
> +monitor commands should never exit().
> +
> +Do not call exit() or abort() to handle an error that can be triggered
> +by the guest (e.g., some unimplemented corner case in guest code
> +translation or device emulation).  Guests should not be able to
> +terminate QEMU.
> +
> +Note that &error_fatal is just another way to exit(1), and &error_abort
> +is just another way to abort().
> +
> +
>  trace-events style
>  ==================
>
> diff --git a/HACKING.rst b/HACKING.rst
> deleted file mode 100644
> index 668fc420c3..0000000000
> --- a/HACKING.rst
> +++ /dev/null
> @@ -1,300 +0,0 @@
> -============
> -QEMU Hacking
> -============
> -
> -.. contents:: Table of Contents
> -
> -Preprocessor
> -============
> -
> -Variadic macros
> ----------------
> -
> -For variadic macros, stick with this C99-like syntax:
> -
> -.. code-block:: c
> -
> -    #define DPRINTF(fmt, ...)                                       \
> -        do { printf("IRQ: " fmt, ## __VA_ARGS__); } while (0)
> -
> -Include directives
> -------------------
> -
> -Order include directives as follows:
> -
> -.. code-block:: c
> -
> -    #include "qemu/osdep.h"  /* Always first... */
> -    #include <...>           /* then system headers... */
> -    #include "..."           /* and finally QEMU headers. */
> -
> -The "qemu/osdep.h" header contains preprocessor macros that affect the 
> behavior
> -of core system headers like <stdint.h>.  It must be the first include so that
> -core system headers included by external libraries get the preprocessor 
> macros
> -that QEMU depends on.
> -
> -Do not include "qemu/osdep.h" from header files since the .c file will have
> -already included it.
> -
> -C types
> -=======
> -
> -It should be common sense to use the right type, but we have collected
> -a few useful guidelines here.
> -
> -Scalars
> --------
> -
> -If you're using "int" or "long", odds are good that there's a better type.
> -If a variable is counting something, it should be declared with an
> -unsigned type.
> -
> -If it's host memory-size related, size_t should be a good choice (use
> -ssize_t only if required). Guest RAM memory offsets must use ram_addr_t,
> -but only for RAM, it may not cover whole guest address space.
> -
> -If it's file-size related, use off_t.
> -If it's file-offset related (i.e., signed), use off_t.
> -If it's just counting small numbers use "unsigned int";
> -(on all but oddball embedded systems, you can assume that that
> -type is at least four bytes wide).
> -
> -In the event that you require a specific width, use a standard type
> -like int32_t, uint32_t, uint64_t, etc.  The specific types are
> -mandatory for VMState fields.
> -
> -Don't use Linux kernel internal types like u32, __u32 or __le32.
> -
> -Use hwaddr for guest physical addresses except pcibus_t
> -for PCI addresses.  In addition, ram_addr_t is a QEMU internal address
> -space that maps guest RAM physical addresses into an intermediate
> -address space that can map to host virtual address spaces.  Generally
> -speaking, the size of guest memory can always fit into ram_addr_t but
> -it would not be correct to store an actual guest physical address in a
> -ram_addr_t.
> -
> -For CPU virtual addresses there are several possible types.
> -vaddr is the best type to use to hold a CPU virtual address in
> -target-independent code. It is guaranteed to be large enough to hold a
> -virtual address for any target, and it does not change size from target
> -to target. It is always unsigned.
> -target_ulong is a type the size of a virtual address on the CPU; this means
> -it may be 32 or 64 bits depending on which target is being built. It should
> -therefore be used only in target-specific code, and in some
> -performance-critical built-per-target core code such as the TLB code.
> -There is also a signed version, target_long.
> -abi_ulong is for the ``*``-user targets, and represents a type the size of
> -'void ``*``' in that target's ABI. (This may not be the same as the size of a
> -full CPU virtual address in the case of target ABIs which use 32 bit pointers
> -on 64 bit CPUs, like sparc32plus.) Definitions of structures that must match
> -the target's ABI must use this type for anything that on the target is 
> defined
> -to be an 'unsigned long' or a pointer type.
> -There is also a signed version, abi_long.
> -
> -Of course, take all of the above with a grain of salt.  If you're about
> -to use some system interface that requires a type like size_t, pid_t or
> -off_t, use matching types for any corresponding variables.
> -
> -Also, if you try to use e.g., "unsigned int" as a type, and that
> -conflicts with the signedness of a related variable, sometimes
> -it's best just to use the *wrong* type, if "pulling the thread"
> -and fixing all related variables would be too invasive.
> -
> -Finally, while using descriptive types is important, be careful not to
> -go overboard.  If whatever you're doing causes warnings, or requires
> -casts, then reconsider or ask for help.
> -
> -Pointers
> ---------
> -
> -Ensure that all of your pointers are "const-correct".
> -Unless a pointer is used to modify the pointed-to storage,
> -give it the "const" attribute.  That way, the reader knows
> -up-front that this is a read-only pointer.  Perhaps more
> -importantly, if we're diligent about this, when you see a non-const
> -pointer, you're guaranteed that it is used to modify the storage
> -it points to, or it is aliased to another pointer that is.
> -
> -Typedefs
> ---------
> -
> -Typedefs are used to eliminate the redundant 'struct' keyword, since type
> -names have a different style than other identifiers ("CamelCase" versus
> -"snake_case").  Each named struct type should have a CamelCase name and a
> -corresponding typedef.
> -
> -Since certain C compilers choke on duplicated typedefs, you should avoid
> -them and declare a typedef only in one header file.  For common types,
> -you can use "include/qemu/typedefs.h" for example.  However, as a matter
> -of convenience it is also perfectly fine to use forward struct
> -definitions instead of typedefs in headers and function prototypes; this
> -avoids problems with duplicated typedefs and reduces the need to include
> -headers from other headers.
> -
> -Reserved namespaces in C and POSIX
> -----------------------------------
> -
> -Underscore capital, double underscore, and underscore 't' suffixes should be
> -avoided.
> -
> -Low level memory management
> -===========================
> -
> -Use of the malloc/free/realloc/calloc/valloc/memalign/posix_memalign
> -APIs is not allowed in the QEMU codebase. Instead of these routines,
> -use the GLib memory allocation routines g_malloc/g_malloc0/g_new/
> -g_new0/g_realloc/g_free or QEMU's qemu_memalign/qemu_blockalign/qemu_vfree
> -APIs.
> -
> -Please note that g_malloc will exit on allocation failure, so there
> -is no need to test for failure (as you would have to with malloc).
> -Calling g_malloc with a zero size is valid and will return NULL.
> -
> -Prefer g_new(T, n) instead of g_malloc(sizeof(T) ``*`` n) for the following
> -reasons:
> -
> -* It catches multiplication overflowing size_t;
> -* It returns T ``*`` instead of void ``*``, letting compiler catch more type 
> errors.
> -
> -Declarations like
> -
> -.. code-block:: c
> -
> -    T *v = g_malloc(sizeof(*v))
> -
> -are acceptable, though.
> -
> -Memory allocated by qemu_memalign or qemu_blockalign must be freed with
> -qemu_vfree, since breaking this will cause problems on Win32.
> -
> -String manipulation
> -===================
> -
> -Do not use the strncpy function.  As mentioned in the man page, it does *not*
> -guarantee a NULL-terminated buffer, which makes it extremely dangerous to 
> use.
> -It also zeros trailing destination bytes out to the specified length.  
> Instead,
> -use this similar function when possible, but note its different signature:
> -
> -.. code-block:: c
> -
> -    void pstrcpy(char *dest, int dest_buf_size, const char *src)
> -
> -Don't use strcat because it can't check for buffer overflows, but:
> -
> -.. code-block:: c
> -
> -    char *pstrcat(char *buf, int buf_size, const char *s)
> -
> -The same limitation exists with sprintf and vsprintf, so use snprintf and
> -vsnprintf.
> -
> -QEMU provides other useful string functions:
> -
> -.. code-block:: c
> -
> -    int strstart(const char *str, const char *val, const char **ptr)
> -    int stristart(const char *str, const char *val, const char **ptr)
> -    int qemu_strnlen(const char *s, int max_len)
> -
> -There are also replacement character processing macros for isxyz and toxyz,
> -so instead of e.g. isalnum you should use qemu_isalnum.
> -
> -Because of the memory management rules, you must use g_strdup/g_strndup
> -instead of plain strdup/strndup.
> -
> -Printf-style functions
> -======================
> -
> -Whenever you add a new printf-style function, i.e., one with a format
> -string argument and following "..." in its prototype, be sure to use
> -gcc's printf attribute directive in the prototype.
> -
> -This makes it so gcc's -Wformat and -Wformat-security options can do
> -their jobs and cross-check format strings with the number and types
> -of arguments.
> -
> -C standard, implementation defined and undefined behaviors
> -==========================================================
> -
> -C code in QEMU should be written to the C99 language specification. A copy
> -of the final version of the C99 standard with corrigenda TC1, TC2, and TC3
> -included, formatted as a draft, can be downloaded from:
> -
> -    `<http://www.open-std.org/jtc1/sc22/WG14/www/docs/n1256.pdf>`_
> -
> -The C language specification defines regions of undefined behavior and
> -implementation defined behavior (to give compiler authors enough leeway to
> -produce better code).  In general, code in QEMU should follow the language
> -specification and avoid both undefined and implementation defined
> -constructs. ("It works fine on the gcc I tested it with" is not a valid
> -argument...) However there are a few areas where we allow ourselves to
> -assume certain behaviors because in practice all the platforms we care about
> -behave in the same way and writing strictly conformant code would be
> -painful. These are:
> -
> -* you may assume that integers are 2s complement representation
> -* you may assume that right shift of a signed integer duplicates
> -  the sign bit (ie it is an arithmetic shift, not a logical shift)
> -
> -In addition, QEMU assumes that the compiler does not use the latitude
> -given in C99 and C11 to treat aspects of signed '<<' as undefined, as
> -documented in the GNU Compiler Collection manual starting at version 4.0.
> -
> -Error handling and reporting
> -============================
> -
> -Reporting errors to the human user
> -----------------------------------
> -
> -Do not use printf(), fprintf() or monitor_printf().  Instead, use
> -error_report() or error_vreport() from error-report.h.  This ensures the
> -error is reported in the right place (current monitor or stderr), and in
> -a uniform format.
> -
> -Use error_printf() & friends to print additional information.
> -
> -error_report() prints the current location.  In certain common cases
> -like command line parsing, the current location is tracked
> -automatically.  To manipulate it manually, use the loc_``*``() from
> -error-report.h.
> -
> -Propagating errors
> -------------------
> -
> -An error can't always be reported to the user right where it's detected,
> -but often needs to be propagated up the call chain to a place that can
> -handle it.  This can be done in various ways.
> -
> -The most flexible one is Error objects.  See error.h for usage
> -information.
> -
> -Use the simplest suitable method to communicate success / failure to
> -callers.  Stick to common methods: non-negative on success / -1 on
> -error, non-negative / -errno, non-null / null, or Error objects.
> -
> -Example: when a function returns a non-null pointer on success, and it
> -can fail only in one way (as far as the caller is concerned), returning
> -null on failure is just fine, and certainly simpler and a lot easier on
> -the eyes than propagating an Error object through an Error ``*````*`` 
> parameter.
> -
> -Example: when a function's callers need to report details on failure
> -only the function really knows, use Error ``*````*``, and set suitable 
> errors.
> -
> -Do not report an error to the user when you're also returning an error
> -for somebody else to handle.  Leave the reporting to the place that
> -consumes the error returned.
> -
> -Handling errors
> ----------------
> -
> -Calling exit() is fine when handling configuration errors during
> -startup.  It's problematic during normal operation.  In particular,
> -monitor commands should never exit().
> -
> -Do not call exit() or abort() to handle an error that can be triggered
> -by the guest (e.g., some unimplemented corner case in guest code
> -translation or device emulation).  Guests should not be able to
> -terminate QEMU.
> -
> -Note that &error_fatal is just another way to exit(1), and &error_abort
> -is just another way to abort().
> diff --git a/README.rst b/README.rst
> index 9ff2877416..7497709291 100644
> --- a/README.rst
> +++ b/README.rst
> @@ -66,7 +66,7 @@ When submitting patches, one common approach is to use 'git
>  format-patch' and/or 'git send-email' to format & send the mail to the
>  address@hidden mailing list. All patches submitted must contain
>  a 'Signed-off-by' line from the author. Patches should follow the
> -guidelines set out in the HACKING.rst and CODING_STYLE.rst files.
> +guidelines set out in the CODING_STYLE.rst file.
>
>  Additional information on submitting patches can be found online via
>  the QEMU website


--
Alex Bennée