[lvm-devel] [PATCH 5/8] Add lvm_vg_get_property() generic vg property function.

[Petr Rockai]

Dave Wysochanski <dwysocha at redhat.com> writes:

> Add a generic VG property function to lvm2app.  Call the internal library
> vg_get_property() function.  Strings are dup'd internally.
> Rework lvm_vg_get_property to return lvm_property_value and require caller
> to check 'is_valid' flag and lvm_errno() for API error.
> Create a 'get_property' function, local to lvm2app, that factors out
> most of the common code that copies the components of lvm_property_type
> into lvm_property_value.  This allows for a 1-line function for each
> of the generic property functions exported by lvm2app.
>
> Signed-off-by: Dave Wysochanski <dwysocha at redhat.com>
Reviewed-by: Petr Rockai <prockai at redhat.com>

I have some suggestions below, but I don't think any of them are
compulsory. I leave the final decision to your discretion. Other than
that, looks ready to go.

> --- a/liblvm/lvm2app.h
> +++ b/liblvm/lvm2app.h
> @@ -139,7 +139,7 @@ typedef struct physical_volume *pv_t;
>  /**
>   * Logical Volume object list.
>   *
> - * Lists of these structures are returned by lvm_vg_list_pvs().
> + * Lists of these structures are returned by lvm_vg_list_lvs().
>   */
>  typedef struct lvm_lv_list {
>  	struct dm_list list;
> @@ -168,6 +168,27 @@ typedef struct lvm_str_list {
>  	const char *str;
>  } lvm_str_list_t;
>  
> +/**
> + * Property Value
> + *
> + * This structure defines a single LVM property value for an LVM object.
> + * The structures are returned by functions such as
> + * lvm_vg_get_property() and lvm_vg_set_property().
> + *
> + * is_settable: indicates whether a 'set' function exists for this property
> + * is_string: indicates whether this property is a string (1) or integer (0)
> + * is_valid: indicates whether 'value' is valid (1) or not (0)
> + */
> +typedef struct lvm_property_value {
> +	unsigned is_settable:1;
> +	unsigned is_string:1;
> +	unsigned is_valid:1;
> +	union {
> +		const char *string;
> +		uint64_t integer;
> +	} value;
> +} lvm_property_value_t;

A is_integer might be useful here, for symmetry. In the client code, it
might not be obvious that !p.is_string means that it is an integer. It
would also improve API extensibility for the future, may we ever run
into a property that's neither string nor integer (although it won't
help with ABI).

> +
>  /*************************** generic lvm handling ***************************/
>  /**
>   * Create a LVM handle.
> @@ -848,6 +869,45 @@ uint64_t lvm_vg_get_max_lv(const vg_t vg);
>   */
>  struct dm_list *lvm_vg_get_tags(const vg_t vg);
>  
> +/**
> + * Get the value of a VG property
> + *
> + * \memberof vg_t
> + *
> + * \param   vg
> + * VG handle obtained from lvm_vg_create() or lvm_vg_open().
> + *
> + * \param   name
> + * Name of property to query.  See vgs man page for full list of properties
> + * that may be queried.
> + *
> + * The memory allocated for a string property value is tied to the vg_t
> + * handle and will be released when lvm_vg_close() is called.
> + *
> + * Example:
> + *      lvm_property_value v;
> + *      char *prop_name = "vg_mda_count";
> + *
> + *      v = lvm_vg_get_property(vg, prop_name);
> + *      if (lvm_errno(libh) || !v.is_valid) {
> + *           // handle error
> + *           printf("Invalid property name or unable to query"
> + *                  "'%s'.\n", prop_name);
> + *           return;
> + *      }
> + *      if (v.is_string)
> + *           printf(", value = %s\n", v.value.string);
> + *	else
> + *           printf(", value = %"PRIu64"\n", v.value.integer);
> + *
> + *
> + * \return
> + * lvm_property_value structure that will contain the current
> + * value of the property.  Caller should check lvm_errno() as well
> + * as 'is_valid' flag before using the value.
> + */
> +struct lvm_property_value lvm_vg_get_property(const vg_t vg, const char *name);
> +
>  /************************** logical volume handling *************************/
>  
>  /**

> --- a/liblvm/lvm_misc.c
> +++ b/liblvm/lvm_misc.c
> @@ -15,6 +15,7 @@
>  #include "lvm2app.h"
>  #include "lvm_misc.h"
>  #include "lib.h"
> +#include "properties.h"
>  
>  struct dm_list *tag_list_copy(struct dm_pool *p, struct dm_list *tag_list)
>  {
> @@ -43,3 +44,36 @@ struct dm_list *tag_list_copy(struct dm_pool *p, struct dm_list *tag_list)
>  	}
>  	return list;
>  }
> +
> +struct lvm_property_value get_property(const pv_t pv, const vg_t vg,
> +				       const lv_t lv, const char *name)
> +{
> +	struct lvm_property_type prop;
> +	struct lvm_property_value v;
> +
> +	prop.id = name;
> +	if (pv) {
> +		if (!pv_get_property(pv, &prop)) {
> +			v.is_valid = 0;
> +			return v;
> +		}
> +	} else if (vg) {
> +		if (!vg_get_property(vg, &prop)) {
> +			v.is_valid = 0;
> +			return v;
> +		}
> +	} else if (lv) {
> +		if (!lv_get_property(lv, &prop)) {
> +			v.is_valid = 0;
> +			return v;
> +		}
> +	}
> +	v.is_settable = prop.is_settable;
> +	v.is_string = prop.is_string;
> +	if (v.is_string)
> +		v.value.string = prop.value.string;
> +	else
> +		v.value.integer = prop.value.integer;
> +	v.is_valid = 1;

Would it be more convenient to say v.is_valid = !lvm_errno(...) here?
That way, the client code would not need to check lvm_errno unless it
cared what went wrong. (The documentation above would need to be
updated, too.)

> +	return v;
> +}

> --- a/liblvm/lvm_misc.h
> +++ b/liblvm/lvm_misc.h
> @@ -17,5 +17,7 @@
>  #include "libdevmapper.h"
>  
>  struct dm_list *tag_list_copy(struct dm_pool *p, struct dm_list *tag_list);
> +struct lvm_property_value get_property(const pv_t pv, const vg_t vg,
> +				       const lv_t lv, const char *name);
>  
>  #endif
> diff --git a/liblvm/lvm_vg.c b/liblvm/lvm_vg.c
> index a09208a..6970910 100644
> --- a/liblvm/lvm_vg.c
> +++ b/liblvm/lvm_vg.c
> @@ -335,6 +335,12 @@ const char *lvm_vg_get_name(const vg_t vg)
>  	return dm_pool_strndup(vg->vgmem, (const char *)vg->name, NAME_LEN+1);
>  }
>  
> +
> +struct lvm_property_value lvm_vg_get_property(const vg_t vg, const char *name)
> +{
> +	return get_property(NULL, vg, NULL, name);
> +}
> +
>  struct dm_list *lvm_list_vg_names(lvm_t libh)
>  {
>  	return get_vgnames((struct cmd_context *)libh, 0);

Yours,
   Petr.