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This patch adds support for time values used in reporting fields.
The raw values are always stored as number of seconds since epoch.
The support that comes with this patch is the basic one which allows
only for recognition of strictly formatted date and time in selection
criteria (the format follows a subset of formats defined by ISO 8601):
date time timezone
date:
YYYY-MM-DD (or shortly YYYYMMDD)
YYYY-MM (shortly YYYYMM), auto DD=1
YYYY, auto MM=01 and DD=01
time:
hh:mm:ss (or shortly hhmmss)
hh:mm (or shortly hhmm), auto ss=0
hh (or shortly hh), auto mm=0, auto ss=0
timezone (always with + or - sign):
+hh:mm or -hh:mm (or shortly +hhmm or -hhmm)
+hh or -hh
Or directly the time (number of seconds) since Epoch (1970-01-01 00:00:00 UTC)
when the number value is prefixed by "@":
@number_of_seconds_since_epoch
This patch also adds aliases for comparison operators
used together with time values which are more intuitive
to use:
since (as alias for >=)
after (as alias for >)
until (as alias for <=)
before (as alias for <)
For example:
$ lvmconfig --type full report/time_format
time_format="%Y-%m-%d %T %z %Z [%s]"
$ lvs -o name,time vg
LV Time
lvol0 2015-06-28 21:25:41 +0200 CEST [1435519541]
lvol1 2015-06-30 03:25:43 +0200 CEST [1435627543]
lvol2 2015-04-26 14:52:20 +0200 CEST [1430052740]
lvol3 2015-06-30 14:52:23 +0200 CEST [1435668743]
$ lvs vg -o name,time -S 'time since "2015-04-26 15:00" && time until "2015-06-30"'
LV Time
lvol0 2015-06-28 21:25:41 +0200 CEST [1435519541]
lvol1 2015-06-30 03:25:43 +0200 CEST [1435627543]
lvol3 2015-06-30 14:52:23 +0200 CEST [1435668743]
$ lvs vg -o name,time -S 'time since "2015-04-26 15:00" && time until "2015-06-30 6:00"'
LV Time
lvol0 2015-06-28 21:25:41 +0200 CEST [1435519541]
lvol1 2015-06-30 03:25:43 +0200 CEST [1435627543]
$ lvs vg -o name,time -S 'time since @1435519541'
LV Time
lvol0 2015-06-28 21:25:41 +0200 CEST [1435519541]
lvol1 2015-06-30 03:25:43 +0200 CEST [1435627543]
lvol3 2015-06-30 14:52:23 +0200 CEST [1435668743]
This is basic time recognition support that is directly a part of
libdevmapper. Recognition of more free-form expressions will be a
part of subsequent patches.
This patch allows for registration and recognition of reserved
values which are ranges, so they're composed of two values actually
to denote the lower and upper bound for the range (stored as an array
with exactly two items to define the boundaries).
Also, this patch allows for flagging reserved values as named-only
which means that such values are not strictly reserved. The strictly
reserved values are reserved values as used before this patch.
Distinction between strictly-reserved and named-only values
is clearly visible with comparisons. Normally, strictly reserved
value is not accounted for if we do "greater than" or "lower than"
comparisons, for example:
1 2 3 ....
|
abc
- we have "abc" as reserved value for field with value "2"
- the value reported for the field is "abc" (or "2", it doesn't matter here)
- the selection we're processing is -S 'field < abc'
- the result of the selection gives nothing as "abc" is strictly
reserved value (bound to "2") and there's no order defined for
it and it would only match if we directly compared the value
(so -S 'field = abc' would match)
With named-only values, the "abc" is named-only value for "2",
so selection -S 'field < abc" is the same as using -S 'field < 2'.
The "abc" is just an alias for some value so the value or its
assigned name can be used equally in selection criteria.
Scenario:
$ vgs -o+vg_mda_copies
VG #PV #LV #SN Attr VSize VFree #VMdaCps
fedora 1 2 0 wz--n- 9.51g 0 unmanaged
vg 16 9 0 wz--n- 1.94g 1.83g 2
$ lvs -o+read_ahead vg/lvol6 vg/lvol7
LV VG Attr LSize Pool Origin Data% Rahead
lvol6 vg Vwi-a-tz-- 1.00g pool lvol5 0.00 auto
lvol7 vg Vwi---tz-k 1.00g pool lvol6 256.00k
Before this patch:
$vgs -o vg_name,vg_mda_copies -S 'vg_mda_copies < unmanaged'
VG #VMdaCps
vg 2
Problem:
Reserved values can be only used with exact match = or !=, not <,<=,>,>=.
In the example above, the "unamanaged" is internally represented as
18446744073709551615, but this should be ignored while not comparing
field directly with "unmanaged" reserved name with = or !=. Users
should not be aware of this internal mapping of the reserved value
name to its internal value and hence it doesn't make sense for such
reserved value to take place in results of <,<=,> and >=.
There's no order defined for reserved values!!! It's a special
*reserved* value that is taken out of the usual value range
of that type.
This is very similar to what we have already fixed with
2f7f6932dc, but it's the other way round
now - we're using reserved value name in selection criteria now
(in the patch 2f7f693, we had concrete value and we compared it
with the reserved value). So this patch completes patch 2f7f693.
This patch also fixes this problem:
$ lvs -o+read_ahead vg/lvol6 vg/lvol7 -S 'read_ahead > 32k'
LV VG Attr LSize Pool Origin Data% Rahead
lvol6 vg Vwi-a-tz-- 1.00g pool lvol5 0.00 auto
lvol7 vg Vwi---tz-k 1.00g pool lvol6 256.00k
Problem:
In the example above, the internal reserved value "auto" is in the
range of selection "> 32k" - it shouldn't match as well. Here the
"auto" is internally represented as MAX_DBL and of course, numerically,
MAX_DBL > 256k. But for users, the reserved value should be uncomparable
to any number so the mapping of the reserved value name to its interna
value is transparent to users. Again, there's no order defined for
reserved values and hence it should never match if using <,<=,>,>=
operators.
This is actually exactly the same problem as already described in
2f7f6932dc, but that patch failed for
size field types because of incorrect internal representation used.
With this patch applied, both problematic scenarios mentioned
above are fixed now:
$ vgs -o vg_name,vg_mda_copies -S 'vg_mda_copies < unmanaged'
(blank)
$ lvs -o+read_ahead vg/lvol6 vg/lvol7 -S 'read_ahead > 32k'
LV VG Attr LSize Pool Origin Rahead
lvol7 vg Vwi---tz-k 1.00g pool lvol6 256.00k
The new dm_report_object_is_selected fn makes it possible to opt whether the
object reported should be displayed on output or not. Also, in addition to
that, it makes it possible to save the result of selection (either 0 or 1).
So dm_report_object_is_selected is simply more general form of object
reporting fn - combinations now allow for:
dm_report_object_is_selected(rh, object, 1, NULL):
This is exactly the original dm_report_object fn and it's fully equal
to it.
dm_report_object_is_selected(rh, object, 0, selected):
Do not display the result on output, but save info whether the object
is selected or not in 'selected' variable.
dm_report_object_is_selected(rh, object, 1, selected):
Display the result on output (if it passes selection criteria) and save
whether the object is selected or not in 'selected' variable.
dm_report_object(rh, object, 0, NULL):
This combination is not allowed - it will end up with internal error.
We're either interested in selection status or we want to display the
result on output or both, but never nothing of the two.
We only checked global per-report-type reserved values for compatibility
with selection code. This patch also adds a check for per-report-field
reserved values. This avoids problems where unsupported report type is
used as reserved value which could cause hard to debug problems
otherwise. So this additional check stops from registering unsupported
and unhandled per-field reserved values.
Registerting such unsupported reserved value is a programmatic error,
so report internal error in this case to stop us from making a mistake
here in the future or even today where STR_LIST fields can't have
reserved values yet.
Under certain circumstances, the selection code can segfault:
$ vgs --select 'pv_name=~/dev/sda' --unbuffered vg0
VG #PV #LV #SN Attr VSize VFree
vg0 6 3 0 wz--n- 744.00m 588.00m
Segmentation fault (core dumped)
The problem here is the use of --ubuffered together with regex used in
selection criteria. If the report output is not buffered, each row is
discarded as soon as it is reported. The bug is in the use of report
handle's memory - in the example above, what happens is:
1) report handle is initialized together with its memory pool
2) selection tree is initialized from selection criteria string
(using the report handle's memory pool!)
2a) this also means the regex is initialized from report handle's mem pool
3) the object (row) is reported
3a) any memory needed for output is intialized out of report handle's mem pool
3b) selection criteria matching is executed - if the regex is checked the
very first time (for the very first row reported), some more memory
allocation happens as regex allocates internal structures "on-demand",
it's allocating from report handle's mem pool (see also step 2a)
4) the report output is executed
5) the object (row) is discarded, meaning discarding all the mem pool
memory used since step 3.
Now, with step 5) we have discarded the regex internal structures from step 3b.
When we execute reporting for another object (row), we're using the same
selection criteria (step 3b), but tihs is second time we're using the regex
and as such, it's already initialized completely. But the regex is missing the
internal structures now as they got discarded in step 5) from previous
object (row) reporting (because we're using "unbuffered" reporting).
To resolve this issue and to prevent any similar future issues where each
object/row memory is discarded after output (the unbuffered reporting) while
selection tree is global for all the object/rows, use separate memory pool
for report's selection.
This patch replaces "struct selection_node *selection_root" in struct
dm_report with new struct selection which contains both "selection_root"
and "mem" for separate mem pool used for selection.
We can change struct dm_report this way as it is not exposed via libdevmapper.
(This patch will have even more meaning for upcoming patches where selection
is used even for non-reporting commands where "internal" reporting and
selection criteria matching happens and where the internal reporting is
not buffered.)
Add new dm_report_compact_fields function to cause report outout
(dm_report_output) to ignore fields which don't have any value set
in any of the rows reported. This provides support for compact report
output where only fields which have something to report are displayed.
Some values are reserved for special purpose like 'undefined', 'unmanaged' etc.
When using >, <, >= and < comparison operators where the range is considered,
do not include reserved values as proper values in this range which
would otherwise result in not so obvious criteria match (as the reserved value is
actually transparent for the user). It's incorrect.
Example scenario:
$ vgs -o vg_name,vg_mda_copies vg1 vg2
VG #VMdaCps
vg1 1
vg2 unmanaged
The "unmanaged" is actually mapped onto reserved value
18446744073709551615 (2^64 - 1) internally.
Such reseved value is already caught on selection criteria input
properly:
$ vgs -o name,vg_mda_copies vg1 vg2 -S 'vg_mda_copies=18446744073709551615'
Numeric value 18446744073709551615 found in selection is reserved.
However, we still need to fix situaton where the reserved value may be
included in resulting range:
Before this patch:
$ vgs -o vg_name,vg_mda_copies vg1 vg2 -S 'vg_mda_copies >= 1'
VG #VMdaCps
vg1 1
vg2 unmanaged
With this patch applied:
$ vgs -o vg_name,vg_mda_copies vg1 vg2 -S 'vg_mda_copies >= 1'
VG #VMdaCps
vg1 1
From the examples above, we can see that without this patch applied,
the vg_mda_copies >= 1 also matched the reserved value 18446744073709551615
(which is represented by the "unamanged" string on report). When
applying the operators, such values must be skipped! They're meant to
be matched only against their string representation only, e.g.:
$ vgs -o name,vg_mda_copies vg1 vg2 -S 'vg_mda_copies=unmanaged'
VG #VMdaCps
vg2 unmanaged
...or any synonyms:
$ vgs -o name,vg_mda_copies vg1 vg2 -S 'vg_mda_copies=undefined'
VG #VMdaCps
vg2 unmanaged
Using "[ ]" operator together with "&&" (or ",") inside causes the
string list to be matched if and only if all the items given match
the value reported and the number of items also match. This is
strict list matching and the original behaviour we already have.
In contrast to that, the new "{ }" operator together with "&&" inside
causes the string list to be matched if and only if all the items given
match the value reported but the number of items don't need to match.
So we can provide a subset in selection criteria and if the subset
is found, it matches.
For example:
$ lvs -o name,tags
LV LV Tags
lvol0 a
lvol1 a,b
lvol2 b,c,x
lvol3 a,b,y
$ lvs -o name,tags -S 'tags=[a,b]'
LV LV Tags
lvol1 a,b
$ lvs -o name,tags -S 'tags={a,b}'
LV LV Tags
lvol1 a,b
lvol3 a,b,y
So in the example above the a,b is subset of a,b,y and therefore
it also matches.
Clearly, when using "||" (or "#") inside, the { } and [ ] is the
same:
$ lvs -o name,tags -S 'tags=[a#b]'
LV LV Tags
lvol0 a
lvol1 a,b
lvol2 b,c,x
lvol3 a,b,y
$ lvs -o name,tags -S 'tags={a#b}'
LV LV Tags
lvol0 a
lvol1 a,b
lvol2 b,c,x
lvol3 a,b,y
Also in addition to the above feature, fix list with single value
matching when using [ ]:
Before this patch:
$ lvs -o name,tags -S 'tags=[a]'
LV LV Tags
lvol0 a
lvol1 a,b
lvol3 a,b,y
With this patch applied:
$ lvs -o name,tags -S 'tags=[a]'
LV LV Tags
lvol0 a
In case neither [] or {} is used, assume {} (the behaviour is not
changed here):
$ lvs -o name,tags -S 'tags=a'
LV LV Tags
lvol0 a
lvol1 a,b
lvol3 a,b,y
So in new terms 'tags=a' is equal to 'tags={a}'.
Change the help heading from 'Common Fields' to 'Special Fields' for
the fields: selected, help, ?
Remove the code that does 'all' processing with these special fields as
each of them changes the behaviour of the command in an undesirable way.
'lvs -o all,selected' was of course just printing help.
(via internal expansion to 'lv_all,common_all')
and if we ignored the help fields, then '-o common_all' would still
pull in 'selected' and change the way rows were output.
In contrast to per-type reserved values that are applied for all fields
of that type, per-field reserved values are only applied for concrete
field only.
Also add 'struct dm_report_field_reserved_value' to libdm for per-field
reserved value definition. This is defined by field number (an index
in the 'fields' array which is given for the dm_report_init_with_selection
function during report initialization) and the value to use for any
of the specified reserved names.
A field where it has no meaning to do any type of comparison is the
implicit "help" or "?" field. The error given was a bit cryptic
before this patch, the FLD_UNCOMPARABLE flag makes it easier to identify
this situation anywhere in the code and provide much better error message.
This flag can be applied to other fields that may appear in the future -
mostly usable for implicit fields as they always have special purpose
(so we're not exporting it in libdevmapper for now - usual reporting
fields don't need this).
Before this patch:
$ vgs -S help=1
dm_report_object: no data assigned to field help
dm_report_object: no data assigned to field help
(...which is true actually, but let's provide something better...)
With this patch applied:
$vgs -S help=1
Selection field is uncomparable: help.
Selection syntax error at 'help=1'.
$vgs -S '(name=vg && help=1) || vg_size > 1g'
Selection field is uncomparable: help.
Selection syntax error at 'help=1) || vg_size > 1g'.
It's better to have implicit fields at the very end of the output
so users can see them without scrolling back if the list of fields
is long (the "help" is also an implicit field now so it should be
easily visible).
We have "help" and "?" defined as implicit fields now. As such, we
don't need to export these names in libdevmapper (as it was introduced
by commit 7c86131233 within this release).
If anyone uses these field names by mistake, the libdevmapper code can
error out correctly if it detects that the set of explicit field names
(the ones supplied by "fields" arg in dm_report_init/dm_report_init_with_selection)
contains any of the implicit field names (the ones defined internally
by libdevmapper itself).
Making "help" and "?" implicit also simplifies code since the
dm_report_init caller (lvm/dmsetup) doesn't need to check on
dm_report_init return whether "help" or "?" was hit while parsing
fields/sort keys in libdevmapper.
The libdevmapper now sets internal "RH_ALREADY_REPORTED" flag
after it reports the "help" or "?" implicit field. Then libdevmapper
itself checks for this flag in dm_report_object and if found,
the actual reporting is skipped (because the "help" implicit field
was reported instead of the actual report).
Fix gcc warnings:
libdm-report.c:1952:5: warning: "end_op_flag_hit" may be used uninitialized in this function [-Wmaybe-uninitialized]
libdm-report.c:2232:28: warning: "custom" may be used uninitialized in this function [-Wmaybe-uninitialized]
And snap_percent is not 0% in dm < 1.10.0 so
don't test comparison with 0% here.
Implicit fields are fields that are registered with the report
and reported internally by libdevmapper itself (compared to explicit
fields that are registered by the layer above libdevmapper - e.g. LVM,
dmsetup...).
The "selected" field is the implicit field (for now the only one)
that reports the result of the selection. Since the selection itself
is the property of the libdevmapper, the upper layer using dm_report_init
can't register this field itself and it must be done directly at
libdevmapper layer.
The "selected" field is internally registered as part of the "common"
report type with id 0x80000000 (the last bit in uin32_t) which is then
reserved (the explicit report types are then checked if they do not
contain this id and if yes, we error out).
This way, the "selected" field is recognized by all libdevmapper users
that initialize the reporting with "dm_report_init_with_selection".
If reporting is initialized with the classical "dm_report_init",
there's no functional change (so the "selected" field is not defined
and it's not recognized).
Make dm_report_init_with_selection to accept an argument with an
array of reserved values where each element contains a triple:
{dm report field type, reserved value, array of strings representing this value}
When the selection is parsed, we always check whether a string
representation of some reserved value is not hit and if it is,
we use the reserved value assigned for this string instead of
trying to parse it as a value of certain field type.
This makes it possible to define selections like:
... --select lv_major=undefined (or -1 or unknown or undef or whatever string representations are registered for this reserved value in the future)
... --select lv_read_ahead=auto
... --select vg_mda_copies=unmanaged
With this, each time the field value of certain type is hit
and when we compare it with the selection, we use the proper
value for comparison.
For now, register these reserved values that are used at the moment
(also more descriptive names are used for the values):
const uint64_t _reserved_number_undef_64 = UINT64_MAX;
const uint64_t _reserved_number_unmanaged_64 = UINT64_MAX - 1;
const uint64_t _reserved_size_auto_64 = UINT64_MAX;
{
{DM_REPORT_FIELD_TYPE_NUMBER, _reserved_number_undef_64, {"-1", "undefined", "undef", "unknown", NULL}},
{DM_REPORT_FIELD_TYPE_NUMBER, _reserved_number_unmanaged_64, {"unmanaged", NULL}},
{DM_REPORT_FIELD_TYPE_SIZE, _reserved_size_auto_64, {"auto", NULL}},
NULL
}
Same reserved value of different field types do not collide.
All arrays are null-terminated.
The list of reserved values is automatically displayed within
selection help output:
Selection operands
------------------
...
Reserved values
---------------
-1, undefined, undef, unknown - Reserved value for undefined numeric value. [number]
unmanaged - Reserved value for unmanaged number of metadata copies in VG. [number]
auto - Reserved value for size that is automatically calculated. [size]
Selection operators
-------------------
...
When the field list is displayed as help for constructing selection
criteria, show also the field value type. This is useful for users
to know what set of operators are allowed for the type - the subsequent
"Selection operands" section in the help output summarize all known
types that can be used in selection.
The "<lvm command> -S/--select help" shows help (including list of fields to match against):
...field list here including the field type name...
Selection operands
------------------
field - Reporting field.
number - Non-negative integer value.
size - Floating point value with units specified.
string - Characters quoted by ' or " or unquoted.
string list - Strings enclosed by [ ] and elements delimited by either
"all items must match" or "at least one item must match" operator.
regular expression - Characters quoted by ' or " or unquoted.
Selection operators
-------------------
Comparison operators:
=~ - Matching regular expression.
!~ - Not matching regular expression.
= - Equal to.
!= - Not equal to.
>= - Greater than or equal to.
> - Greater than
<= - Less than or equal to.
< - Less than.
Logical and grouping operators:
&& - All fields must match
, - All fields must match
|| - At least one field must match
# - At least one field must match
! - Logical negation
( - Left parenthesis
) - Right parenthesis
[ - List start
] - List end
Selection list items are enclosed in '[' and ']' (if there's only
one item, the '[' and ']' can be omitted). Each element of the list
is a string (either quoted or unquoted, like the usual string operand
used in selection) and each element is delimited either by conjunction
(meaining "match all") or disjunction operator (meaning "match any").
For example, if "," is the conjuction operator and "/" is the
disjunction operator then:
lv_tags=[a,b,c]
...will match all fields where tags contain *all* a, b and c.
lv_tags=[a/b/c]
...will match all fields where tags contain *any* of a, b, or c.
Mixing operators within the list is not supported:
lv_tags=[a,b/c]
...will give an error.
The order in which items are defined in the selection do not matter.
This patch enhances the selection parsing functionality to recognize
such lists.
The {pv,vg,lv,seg}_tags and lv_modules fields are reported as string
lists using the new dm_report_field_string_list - so we just pass
the list to the fn that takes care of reporting and item sorting itself.
Add a separate dm_report_field_string_list fn to libdevmapper to
support reporting string lists. Before, the code used libdevmappers's
dm_report_field_string fn which required formatting the list to a
single string. This functionality is now moved to libdevmapper
and the code that needs to report the string list just needs
to pass the list itself and libdevmapper will take care of this.
This also enhances code reuse.
The dm_report_field_string_list also accepts an argument to define
custom delimiter to use. If not defined, a default "," (comma) is
used as item delimiter in the string list reported.
The dm_report_field_string_list automatically sorts the items in
the list before formatting it to a final string. It also encodes
the position and length within the final string where each element
can be found. This can be used to support checking against each
list item reported since since when formatted as a single string
for the actual report, we would lose this information otherwise
(we don't want to copy each item, the position and length within
the final string is enough for us to get the original items back).
When such lists are checked against the selection tree, we can check
each item individually this way and we can support operators like
"match any" and "match all".
This is rebased and edited version of the original design and
patch proposed by Jun'ichi Nomura:
http://www.redhat.com/archives/dm-devel/2007-April/msg00025.html
The dm_report_init_with_selection is the same as dm_report_init
but it contains an additional argument to set the selection
in the form of a string that contains field names to check against and
selection operators. The selection string is parsend and a selection
tree is composed for use in the checks against individual fields when
the report is processed. The parsed selection tree is stored in dm_report
structure as "selection_root".
This is rebased and edited version of the original design and
patch proposed by Jun'ichi Nomura:
http://www.redhat.com/archives/dm-devel/2007-April/msg00025.html
Add support for parsing numbers, strings (quoted or unquoted), regexes
and operators amogst these operands in selection condition supplied.
This is rebased and edited version of the original design and
patch proposed by Jun'ichi Nomura:
http://www.redhat.com/archives/dm-devel/2007-April/msg00025.html
This patch defines operators and structures that will be used
to store the report selection against which the actual values
reported will be checked.
Selection operators
-------------------
Comparison operators:
=~ - Matching regular expression.
!~ - Not matching regular expression.
= - Equal to.
!= - Not equal to.
>= - Greater than or equal to.
> - Greater than
<= - Less than or equal to.
< - Less than.
Logical and grouping operators:
&& - All fields must match
, - All fields must match
|| - At least one field must match
# - At least one field must match
! - Logical negation
( - Left parenthesis
) - Right parenthesis
This makes it easier to check against the fields (following patches for
report selection) and check whether size units are allowed or not
with the field value.
Share DM_REPORT_FIELD_RESERVED_NAME_{HELP,HELP_ALT} between libdm and
any libdm user to handle reserved field names, in this case the virtual
field name to show help instead of failing on unrecognized field.
The libdm user also needs to check the field name so it can fire
proper code in this case (cleanup, exit etc.).
Add internal error warning when string value is used
as sort value for numerical field.
Using log_warn since the function itself does not return error,
so we do not confuse log_error() checker.
Use log_warn to print non-fatal warning messages.
Use of log_error would confuse checker for testing
whether proper error has been reported for some real error.
Adding couple INTERNAL_ERROR reports for unwanted parameters:
Ensure the 'top' metadata node cannot be NULL for lvmetad.
Make obvious vginfo2 cannot be NULL.
Report internal error if handler and vg is undefined.
Check for handle in poll_vg().
Ensure seg is not NULL in dev_manager_transient().
Report missing read_ahead for _lv_read_ahead_single().
Check for report handler in dm_report_object().
Check missing VG in _vgreduce_single().
As dm_report_field_string() doesn't modify content of data pointer,
it can be marked as const.
It's slight API change - but doesn't require any change on the user side
and supports wider range of arguments without const casting.
(i.e. we may use as paramater const lv struct this way: &lv->name)
Fix assert abort of dmsetup (when compiled with pool debug)
dmsetup splitname --nameprefixes --noheadings --rows gvg-a2
Move pool begin in the inner loop - otherwise it would using
already 'ended' pool object.
Fix memory leak of field_id in _output_field function.
There's been a patch added recently to use dynamic allocation for metadata
tags buffer to remove the 4k limit (for writing metadata out). However, when
using reporting commands like vgs and lvs, we still need to fix libdm reporting
functions themselves to support such long outputs. So the buffer used in those
reporting functions is dynamic now.
The patch also includes a fix for field_id memory leak which was found in
the _output_field function.
When reporting explicitly label attributes (pv_uuid for example), we do not
need to read metadata.
This patch separate the label fileds and removes scan_vgs_for_pvs
in process_each_pv() if not needed.
(There should be no user visible change in output.)
In libdm, we only ever use 'fields', while the tools use 'options' and
'fields' interchangeably.
Ideally it would be good to use 'fields' consistently everywhere.
However, 'options' most likely comes from the tool commandline '-o' and
'--options' which cannot be changed.
For example in LVM2, "pv_all" gives all PV fields.
"seg_all" gives all LV segment fields.
"all" gives all fields of the final report type. I think this is more
useful than just adding the current prefix.
So "lvs -o seg_all" gives all the LV segment fields, whilst
"lvs --segments -o all" adds in LV and VG fields too.
"lvs -o all -O vg_name" has report type LVS+VGS so includes all LV and all
VG fields.
