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libdm: clarify library's use of aux_data

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Make it clear in libdevmapper.h, and in function argument names, that
libdm-stats uses the aux_data field internally and that any values set
for user_data are appended to the library values before being stored
with a region, and similarly, that internal data fields will be stripped
prior to returning any previously stored user_data.
This commit is contained in:
Bryn M. Reeves 2016-07-05 15:17:44 +01:00
parent 2b0dd0b051
commit fef4832a85
2 changed files with 48 additions and 14 deletions
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58
libdm/libdevmapper.h
View File

@ -638,9 +638,24 @@ int dm_stats_populate(struct dm_stats *dms, const char *program_id,
* program creating the region. If program_id is NULL or the empty
* string the default program_id stored in the handle will be used.
*
* aux_data is an optional string argument passed to the kernel that is
* stored with the statistics region. It is not currently accessed by
* the library or kernel and may be used to store arbitrary user data.
* user_data is an optional string argument that is added to the
* content of the aux_data field stored with the statistics region by
* the kernel.
*
* The library may also use this space internally, for example, to
* store a group descriptor or other metadata: in this case the
* library will strip any internal data fields from the value before
* it is returned via a call to dm_stats_get_region_aux_data().
*
* The user data stored is not accessed by the library or kernel and
* may be used to store an arbitrary data word (embedded whitespace is
* not permitted).
*
* An application using both the library and direct access to the
* @stats_list device-mapper message may see the internal values stored
* in this field by the library. In such cases any string up to and
* including the first '#' in the field must be treated as an opaque
* value and preserved across any external modification of aux_data.
*
* The region_id of the newly-created region is returned in *region_id
* if it is non-NULL.
@ -648,7 +663,7 @@ int dm_stats_populate(struct dm_stats *dms, const char *program_id,
int dm_stats_create_region(struct dm_stats *dms, uint64_t *region_id,
uint64_t start, uint64_t len, int64_t step,
int precise, struct dm_histogram *bounds,
const char *program_id, const char *aux_data);
const char *program_id, const char *user_data);
/*
* Delete the specified statistics region. This will also mark the
@ -922,16 +937,35 @@ int dm_stats_get_area_offset(const struct dm_stats *dms, uint64_t *offset,
uint64_t region_id, uint64_t area_id);
/*
* Retrieve program_id and aux_data for a specific region. Only valid
* following a call to dm_stats_list(). The returned pointer does not
* need to be freed separately from the dm_stats handle but will become
* invalid after a dm_stats_destroy(), dm_stats_list(),
* dm_stats_populate(), or dm_stats_bind*() of the handle from which it
* was obtained.
* Retrieve program_id and user aux_data for a specific region.
*
* Only valid following a call to dm_stats_list().
*/
/*
* Retrieve program_id for the specified region.
*
* The returned pointer does not need to be freed separately from the
* dm_stats handle but will become invalid after a dm_stats_destroy(),
* dm_stats_list(), dm_stats_populate(), or dm_stats_bind*() of the
* handle from which it was obtained.
*/
const char *dm_stats_get_region_program_id(const struct dm_stats *dms,
uint64_t region_id);
/*
* Retrieve user aux_data set for the specified region. This function
* will return any stored user aux_data as a string in the memory
* pointed to by the aux_data argument.
*
* Any library internal aux_data fields, such as DMS_GROUP descriptors,
* are stripped before the value is returned.
*
* The returned pointer does not need to be freed separately from the
* dm_stats handle but will become invalid after a dm_stats_destroy(),
* dm_stats_list(), dm_stats_populate(), or dm_stats_bind*() of the
* handle from which it was obtained.
*/
const char *dm_stats_get_region_aux_data(const struct dm_stats *dms,
uint64_t region_id);
@ -1184,8 +1218,8 @@ int dm_stats_get_current_area_len(const struct dm_stats *dms,
const char *dm_stats_get_current_region_program_id(const struct dm_stats *dms);
/*
* Return a pointer to the aux_data string for the region at the current
* cursor location.
* Return a pointer to the user aux_data string for the region at the
* current cursor location.
*/
const char *dm_stats_get_current_region_aux_data(const struct dm_stats *dms);

4
libdm/libdm-stats.c
View File

@ -1930,7 +1930,7 @@ out:
int dm_stats_create_region(struct dm_stats *dms, uint64_t *region_id,
uint64_t start, uint64_t len, int64_t step,
int precise, struct dm_histogram *bounds,
const char *program_id, const char *aux_data)
const char *program_id, const char *user_data)
{
char *hist_arg = NULL;
int r = 0;
@ -1946,7 +1946,7 @@ int dm_stats_create_region(struct dm_stats *dms, uint64_t *region_id,
}
r = _stats_create_region(dms, region_id, start, len, step,
precise, hist_arg, program_id, aux_data);
precise, hist_arg, program_id, user_data);
dm_free(hist_arg);
out: