I resend this patch, this time adding Jaroslav Kysela and Takashi Iwai to CC.
I added doxygen documentation to alsa-lib. The patch was created using git format-patch.
This is my first patch. Please let me know if I need to improve it.
From 731895b67fcae743551989a5dd04382003e66560 Mon Sep 17 00:00:00 2001
From: "Tanjeff-N. Moos" tanjeff@cccmz.de Date: Fri, 14 Aug 2020 08:40:28 +0200 Subject: [PATCH] Add documentation for snd_ctl_elem_list_*.
--- include/control.h | 81 +++++++++++++++++++++++++++++++++++++++++-- src/control/control.c | 80 ++++++++++++++++++++++++++++++++++++------ 2 files changed, 148 insertions(+), 13 deletions(-)
diff --git a/include/control.h b/include/control.h index 02db72d4..9deec6f3 100644 --- a/include/control.h +++ b/include/control.h @@ -56,7 +56,75 @@ typedef struct _snd_ctl_card_info snd_ctl_card_info_t; /** CTL element identifier container */ typedef struct _snd_ctl_elem_id snd_ctl_elem_id_t;
-/** CTL element identifier list container */ +/** CTL element list container + * + * This is a list of CTL elements. The list contains management + * information (e.g. how many elements the sound card has) as well as + * the element identifiers. All functions which operate on the list + * are named snd_ctl_elem_list_*(). + * + * \par Memory management + * + * There are two memory areas to deal with: The list container itself + * and the memory for the element identifiers. + * + * To manage the area for the list container, the following functions + * are used: + * + * - snd_ctl_elem_list_malloc() / snd_ctl_elem_list_free() to allocate + * and free memory on the heap, or + * - snd_ctl_elem_list_alloca() to allocate the memory on the + * stack. This memory is auto-released when the stack is unwound. + * + * To manage the space for the element identifiers, the + * snd_ctl_elem_list_alloc_space() and snd_ctl_elem_list_free_space() + * are used. Allocating the right amount of space can be achieved by + * first obtaining the number of elements and then calling + * snd_ctl_elem_list_alloc_space(): + * + * \code + * snd_ctl_elem_list_t* list; + * int count; + * + * // Initialise list + * snd_ctl_elem_list_malloc(&list); + * + * // Get number of elements + * snd_ctl_elem_list(ctl, list); + * count = snd_ctl_elem_list_get_count(list); + * + * // Allocate space for identifiers + * snd_ctl_elem_list_alloc_space(list, count); + * + * // Get identifiers + * snd_ctl_elem_list(ctl, list); // yes, this is same as above + * + * // Do something useful with the list... + * + * // Cleanup + * snd_ctl_elem_list_free_space(list); + * snd_ctl_elem_list_free(list); + * \endcode + * + * + * \par The Elements + * + * The elements in the list are accessed using an index. This index is + * the location in the list; Don't confuse it with the 'index' of the + * element identifier. For example: + * + * \code + * snd_ctl_elem_list_t list; + * unsigned int element_index; + * + * // Allocate space, fill list ... + * + * element_index = snd_ctl_elem_list_get_index(&list, 2); + * \endcode + * + * This will access the 3rd element in the list (index=2) and get the + * elements index from the driver (which might be 13, for example). + */ typedef struct _snd_ctl_elem_list snd_ctl_elem_list_t;
/** CTL element info container */ @@ -354,11 +422,18 @@ void snd_ctl_event_copy(snd_ctl_event_t *dst, const snd_ctl_event_t *src); snd_ctl_event_type_t snd_ctl_event_get_type(const snd_ctl_event_t *obj);
size_t snd_ctl_elem_list_sizeof(void); + /** \hideinitializer - * \brief allocate an invalid #snd_ctl_elem_list_t using standard alloca - * \param ptr returned pointer + * + * \brief Allocate a #snd_ctl_elem_list_t using standard alloca. + * + * The memory is allocated on the stack and will automatically be + * released when the stack unwinds (i.e. no free() is needed). + * + * \param ptr Pointer to allocated memory. */ #define snd_ctl_elem_list_alloca(ptr) __snd_alloca(ptr, snd_ctl_elem_list) + int snd_ctl_elem_list_malloc(snd_ctl_elem_list_t **ptr); void snd_ctl_elem_list_free(snd_ctl_elem_list_t *obj); void snd_ctl_elem_list_clear(snd_ctl_elem_list_t *obj); diff --git a/src/control/control.c b/src/control/control.c index e21e8f1d..1bcf1ab2 100644 --- a/src/control/control.c +++ b/src/control/control.c @@ -280,6 +280,21 @@ int snd_ctl_card_info(snd_ctl_t *ctl, snd_ctl_card_info_t *info)
/** * \brief Get a list of element identifiers + * + * Before calling this function, memoru must be allocated using + * snd_ctl_elem_list_malloc(). + * + * This function obtains data from the sound card driver and puts it + * into the list. + * + * If there was space allocated for the element identifiers (using + * snd_ctl_elem_list_alloc_space()), information will be filled in. If + * too little space was allocated, only a part of the elements will be + * queried. If there was too much space allocated, some of it remains + * unused. Use snd_ctl_elem_list_get_count() and + * snd_ctl_elem_list_get_used() to obtain information about space + * usage. See #snd_ctl_elem_list_t to learn more. + * * \param ctl CTL handle * \param list CTL element identifiers list pointer * \return 0 on success otherwise a negative error code @@ -1508,9 +1523,14 @@ const char *snd_ctl_event_type_name(snd_ctl_event_type_t type)
/** * \brief allocate space for CTL element identifiers list - * \param obj CTL element identifiers list - * \param entries Entries to allocate - * \return 0 on success otherwise a negative error code + * + * The space can be released with snd_ctl_elem_list_free_space(). + * + * \param obj CTL element identifiers list. + * \param entries How many entries to allocate. See + * #snd_ctl_elem_list_t to learn how to obtain + * this number in advance. + * \return 0 on success otherwise a negative error code. */ int snd_ctl_elem_list_alloc_space(snd_ctl_elem_list_t *obj, unsigned int entries) { @@ -1526,6 +1546,10 @@ int snd_ctl_elem_list_alloc_space(snd_ctl_elem_list_t *obj, unsigned int entries
/** * \brief free previously allocated space for CTL element identifiers list + * + * Releases space previously allocated using + * snd_ctl_elem_list_alloc_space(). + * * \param obj CTL element identifiers list */ void snd_ctl_elem_list_free_space(snd_ctl_elem_list_t *obj) @@ -2016,7 +2040,7 @@ snd_ctl_event_type_t snd_ctl_event_get_type(const snd_ctl_event_t *obj) }
/** - * \brief get size of #snd_ctl_elem_list_t + * \brief get size of #snd_ctl_elem_list_t. * \return size in bytes */ size_t snd_ctl_elem_list_sizeof() @@ -2025,7 +2049,10 @@ size_t snd_ctl_elem_list_sizeof() }
/** - * \brief allocate an invalid #snd_ctl_elem_list_t using standard malloc + * \brief allocate a #snd_ctl_elem_list_t using standard malloc. + * + * The memory can be released using snd_ctl_elem_list_free(). + * * \param ptr returned pointer * \return 0 on success otherwise negative error code */ @@ -2039,7 +2066,15 @@ int snd_ctl_elem_list_malloc(snd_ctl_elem_list_t **ptr) }
/** - * \brief frees a previously allocated #snd_ctl_elem_list_t + * \brief frees a previously allocated #snd_ctl_elem_list_t. + * + * Release memory previously allocated using + * snd_ctl_elem_list_malloc(). + * + * If you used snd_ctl_elem_list_alloc_space() on the list, you must + * use snd_ctl_elem_list_free_space() \em before calling this + * function. + * * \param obj pointer to object to free */ void snd_ctl_elem_list_free(snd_ctl_elem_list_t *obj) @@ -2048,7 +2083,15 @@ void snd_ctl_elem_list_free(snd_ctl_elem_list_t *obj) }
/** - * \brief clear given #snd_ctl_elem_list_t object + * \brief Clear given #snd_ctl_elem_list_t object. + * + * This will make the stored identifiers inaccessible without freeing + * their space. + * + * \warning The element identifier space cannot be freed after calling + * this function. Therefore, snd_ctl_elem_list_free_space() + * must be called in advance. + * * \param obj pointer to object to clear */ void snd_ctl_elem_list_clear(snd_ctl_elem_list_t *obj) @@ -2057,7 +2100,11 @@ void snd_ctl_elem_list_clear(snd_ctl_elem_list_t *obj) }
/** - * \brief copy one #snd_ctl_elem_list_t to another + * \brief copy one #snd_ctl_elem_list_t to another. + * + * This performs a shallow copy. That means the both lists will share + * the same space for the elements. The elements will not be copied. + * * \param dst pointer to destination * \param src pointer to source */ @@ -2080,6 +2127,12 @@ void snd_ctl_elem_list_set_offset(snd_ctl_elem_list_t *obj, unsigned int val)
/** * \brief Get number of used entries in CTL element identifiers list + * + * This function returns how many entries are actually filled with + * useful information. + * + * See also snd_ctl_elem_list_get_count(). + * * \param obj CTL element identifier list * \return number of used entries */ @@ -2090,7 +2143,14 @@ unsigned int snd_ctl_elem_list_get_used(const snd_ctl_elem_list_t *obj) }
/** - * \brief Get total count of elements present in CTL device (information present in every filled CTL element identifiers list) + * \brief Get total count of elements present in CTL device + * + * This function returns how many entries were allocated using + * snd_ctl_elem_list_alloc_space(). This information is present after + * snd_ctl_elem_list() was called. + * + * See also snd_ctl_elem_list_get_used(). + * * \param obj CTL element identifier list * \return total number of elements */ @@ -2140,7 +2200,7 @@ snd_ctl_elem_iface_t snd_ctl_elem_list_get_interface(const snd_ctl_elem_list_t * }
/** - * \brief Get device part of CTL element identifier for an entry of a CTL element identifiers list + * \brief Get the device part of CTL element identifier for an entry of a CTL element identifiers list * \param obj CTL element identifier list * \param idx Index of entry * \return CTL element related device