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Add the virStrncpy function, which takes a dst string, source string, the number of bytes to copy and the number of bytes available in the dest string. If the source string is too large to fit into the destination string, including the \0 byte, then no data is copied and the function returns NULL. Otherwise, this function copies n bytes from source into dst, including the \0, and returns a pointer to the dst string. This function is intended to replace all unsafe uses of strncpy in the code base, since strncpy does *not* guarantee that the buffer terminates with a \0. Signed-off-by: Chris Lalancette <clalance@redhat.com>
383 lines
12 KiB
Plaintext
383 lines
12 KiB
Plaintext
Libvirt contributor guidelines
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==============================
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General tips for contributing patches
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=====================================
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(1) Discuss any large changes on the mailing list first. Post patches
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early and listen to feedback.
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(2) Post patches in unified diff format. A command similar to this
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should work:
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diff -urp libvirt.orig/ libvirt.modified/ > libvirt-myfeature.patch
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or:
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cvs diff -up > libvirt-myfeature.patch
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(3) Split large changes into a series of smaller patches, self-contained
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if possible, with an explanation of each patch and an explanation of how
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the sequence of patches fits together.
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(4) Make sure your patches apply against libvirt CVS. Developers
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only follow CVS and don't care much about released versions.
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(5) Run the automated tests on your code before submitting any changes.
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In particular, configure with compile warnings set to -Werror:
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./configure --enable-compile-warnings=error
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and run the tests:
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make check
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make syntax-check
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make -C tests valgrind
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The latter test checks for memory leaks.
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(6) Update tests and/or documentation, particularly if you are adding
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a new feature or changing the output of a program.
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There is more on this subject, including lots of links to background
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reading on the subject, on this page:
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http://et.redhat.com/~rjones/how-to-supply-code-to-open-source-projects/
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Code indentation
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================
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Libvirt's C source code generally adheres to some basic code-formatting
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conventions. The existing code base is not totally consistent on this
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front, but we do prefer that contributed code be formatted similarly.
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In short, use spaces-not-TABs for indentation, use 4 spaces for each
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indentation level, and other than that, follow the K&R style.
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If you use Emacs, add the following to one of one of your start-up files
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(e.g., ~/.emacs), to help ensure that you get indentation right:
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;;; When editing C sources in libvirt, use this style.
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(defun libvirt-c-mode ()
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"C mode with adjusted defaults for use with libvirt."
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(interactive)
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(c-set-style "K&R")
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(setq indent-tabs-mode nil) ; indent using spaces, not TABs
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(setq c-indent-level 4)
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(setq c-basic-offset 4))
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(add-hook 'c-mode-hook
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'(lambda () (if (string-match "/libvirt" (buffer-file-name))
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(libvirt-c-mode))))
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Code formatting (especially for new code)
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=========================================
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With new code, we can be even more strict.
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Please apply the following function (using GNU indent) to any new code.
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Note that this also gives you an idea of the type of spacing we prefer
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around operators and keywords:
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indent-libvirt()
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{
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indent -bad -bap -bbb -bli4 -br -ce -brs -cs -i4 -l75 -lc75 \
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-sbi4 -psl -saf -sai -saw -sbi4 -ss -sc -cdw -cli4 -npcs -nbc \
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--no-tabs "$@"
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}
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Note that sometimes you'll have to postprocess that output further, by
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piping it through "expand -i", since some leading TABs can get through.
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Usually they're in macro definitions or strings, and should be converted
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anyhow.
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C types
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=======
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Use the right type.
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Scalars
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-------
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If you're using "int" or "long", odds are good that there's a better type.
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If a variable is counting something, be sure to declare it with an
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unsigned type.
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If it's memory-size-related, use size_t (use ssize_t only if required).
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If it's file-size related, use uintmax_t, or maybe off_t.
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If it's file-offset related (i.e., signed), use off_t.
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If it's just counting small numbers use "unsigned int";
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(on all but oddball embedded systems, you can assume that that
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type is at least four bytes wide).
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If a variable has boolean semantics, give it the "bool" type
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and use the corresponding "true" and "false" macros. It's ok
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to include <stdbool.h>, since libvirt's use of gnulib ensures
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that it exists and is usable.
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In the unusual event that you require a specific width, use a
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standard type like int32_t, uint32_t, uint64_t, etc.
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While using "bool" is good for readability, it comes with minor caveats:
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- Don't use "bool" in places where the type size must be constant across
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all systems, like public interfaces and on-the-wire protocols. Note
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that it would be possible (albeit wasteful) to use "bool" in libvirt's
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logical wire protocol, since XDR maps that to its lower-level bool_t
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type, which *is* fixed-size.
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- Don't compare a bool variable against the literal, "true",
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since a value with a logical non-false value need not be "1".
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I.e., don't write "if (seen == true) ...". Rather, write "if (seen)...".
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Of course, take all of the above with a grain of salt. If you're about
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to use some system interface that requires a type like size_t, pid_t or
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off_t, use matching types for any corresponding variables.
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Also, if you try to use e.g., "unsigned int" as a type, and that
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conflicts with the signedness of a related variable, sometimes
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it's best just to use the *wrong* type, if "pulling the thread"
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and fixing all related variables would be too invasive.
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Finally, while using descriptive types is important, be careful not to
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go overboard. If whatever you're doing causes warnings, or requires
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casts, then reconsider or ask for help.
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Pointers
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--------
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Ensure that all of your pointers are "const-correct".
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Unless a pointer is used to modify the pointed-to storage,
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give it the "const" attribute. That way, the reader knows
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up-front that this is a read-only pointer. Perhaps more
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importantly, if we're diligent about this, when you see a non-const
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pointer, you're guaranteed that it is used to modify the storage
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it points to, or it is aliased to another pointer that is.
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Low level memory management
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===========================
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Use of the malloc/free/realloc/calloc APIs is deprecated in the libvirt
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codebase, because they encourage a number of serious coding bugs and do
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not enable compile time verification of checks for NULL. Instead of these
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routines, use the macros from memory.h
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- eg to allocate a single object:
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virDomainPtr domain;
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if (VIR_ALLOC(domain) < 0) {
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__virRaiseError(VIR_ERROR_NO_MEMORY)
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return NULL;
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}
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- eg to allocate an array of objects
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virDomainPtr domains;
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int ndomains = 10;
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if (VIR_ALLOC_N(domains, ndomains) < 0) {
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__virRaiseError(VIR_ERROR_NO_MEMORY)
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return NULL;
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}
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- eg to allocate an array of object pointers
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virDomainPtr *domains;
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int ndomains = 10;
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if (VIR_ALLOC_N(domains, ndomains) < 0) {
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__virRaiseError(VIR_ERROR_NO_MEMORY)
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return NULL;
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}
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- eg to re-allocate the array of domains to be longer
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ndomains = 20
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if (VIR_REALLOC_N(domains, ndomains) < 0) {
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__virRaiseError(VIR_ERROR_NO_MEMORY)
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return NULL;
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}
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- eg to free the domain
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VIR_FREE(domain);
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String comparisons
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==================
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Do not use the strcmp, strncmp, etc functions directly. Instead use
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one of the following semantically named macros
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- For strict equality:
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STREQ(a,b)
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STRNEQ(a,b)
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- For case sensitive equality:
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STRCASEEQ(a,b)
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STRCASENEQ(a,b)
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- For strict equality of a substring:
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STREQLEN(a,b,n)
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STRNEQLEN(a,b,n)
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- For case sensitive equality of a substring:
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STRCASEEQLEN(a,b,n)
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STRCASENEQLEN(a,b,n)
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- For strict equality of a prefix:
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STRPREFIX(a,b)
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String copying
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==============
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Do not use the strncpy function. According to the man page, it does
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*not* guarantee a NULL-terminated buffer, which makes it extremely dangerous
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to use. Instead, use one of the functionally equivalent functions:
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- virStrncpy(char *dest, const char *src, size_t n, size_t destbytes)
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The first three arguments have the same meaning as for strncpy; namely the
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destination, source, and number of bytes to copy, respectively. The last
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argument is the number of bytes available in the destination string; if a
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copy of the source string (including a \0) will not fit into the
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destination, no bytes are copied and the routine returns NULL.
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Otherwise, n bytes from the source are copied into the destination and a
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trailing \0 is appended.
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- virStrcpy(char *dest, const char *src, size_t destbytes)
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Use this variant if you know you want to copy the entire src string
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into dest. Note that this is a macro, so arguments could be
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evaluated more than once. This is equivalent to
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virStrncpy(dest, src, strlen(src), destbytes)
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- virStrcpyStatic(char *dest, const char *src)
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Use this variant if you know you want to copy the entire src string
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into dest *and* you know that your destination string is a static string
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(i.e. that sizeof(dest) returns something meaningful). Note that
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this is a macro, so arguments could be evaluated more than once. This is
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equivalent to virStrncpy(dest, src, strlen(src), sizeof(dest)).
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Variable length string buffer
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=============================
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If there is a need for complex string concatenations, avoid using
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the usual sequence of malloc/strcpy/strcat/snprintf functions and
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make use of the virBuffer API described in buf.h
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eg typical usage is as follows:
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char *
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somefunction(...) {
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virBuffer buf = VIR_BUFFER_INITIALIZER;
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...
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virBufferAddLit(&buf, "<domain>\n");
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virBufferVSprint(&buf, " <memory>%d</memory>\n", memory);
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...
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virBufferAddLit(&buf, "</domain>\n");
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....
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if (virBufferError(&buf)) {
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__virRaiseError(...);
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return NULL;
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}
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return virBufferContentAndReset(&buf);
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}
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Include files
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=============
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There are now quite a large number of include files, both libvirt
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internal and external, and system includes. To manage all this
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complexity it's best to stick to the following general plan for all
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*.c source files:
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/*
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* Copyright notice
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* ....
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* ....
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* ....
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*
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*/
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#include <config.h> Must come first in every file.
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#include <stdio.h> Any system includes you need.
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#include <string.h>
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#include <limits.h>
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#if HAVE_NUMACTL Some system includes aren't supported
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#include <numa.h> everywhere so need these #if defences.
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#endif
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#include "internal.h" Include this first, after system includes.
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#include "util.h" Any libvirt internal header files.
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#include "buf.h"
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static myInternalFunc () The actual code.
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{
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...
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Of particular note: *DO NOT* include libvirt/libvirt.h or
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libvirt/virterror.h. It is included by "internal.h" already and there
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are some special reasons why you cannot include these files
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explicitly.
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Printf-style functions
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======================
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Whenever you add a new printf-style function, i.e., one with a format
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string argument and following "..." in its prototype, be sure to use
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gcc's printf attribute directive in the prototype. For example, here's
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the one for virAsprintf, in util.h:
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int virAsprintf(char **strp, const char *fmt, ...)
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ATTRIBUTE_FMT_PRINTF(2, 3);
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This makes it so gcc's -Wformat and -Wformat-security options can do
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their jobs and cross-check format strings with the number and types
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of arguments.
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Libvirt commiters guidelines
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============================
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The AUTHORS files indicates the list of people with commit acces right
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who can actually merge the patches.
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The general rule for commiting patches is to make sure it has been reviewed
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properly in the mailing-list first, usually if a couple of persons gave an
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ACK or +1 to a patch and nobody raised an objection on the list it should
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be good to go. If the patch touches a part of the code where you're not the
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main maintainer or not have a very clear idea of how things work, it's better
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to wait for a more authoritative feedback though. Before commiting please
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also rebuild locally and run 'make check syntax-check' and make sure they
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don't raise error. Try to look for warnings too for example configure with
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--enable-compile-warnings=error
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which adds -Werror to compile flags, so no warnings get missed
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Exceptions to that 'review and approval on the list first' is fixing failures
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to build:
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- if a recently commited patch breaks compilation on a platform
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or for a given driver then it's fine to commit a minimal fix
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directly without getting the review feedback first
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- similary if make check or make syntax-chek breaks, if there is
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an obvious fix, it's fine to commit immediately
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The patch should still be sent to the list (or tell what the fix was if
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trivial) and 'make check syntax-check' should pass too before commiting
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anything
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Similary fixes for documentation and code comments can be managed
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in the same way, but still make sure they get reviewed if non-trivial.
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