This patch introduces a function that will allow us to resolve a
relative difference between two elements of a disk backing chain. This
function will be used to allow relative block commit and block pull
where we need to specify the new relative name of the image to qemu.

This patch also adds unit tests for the function to verify that it works
correctly.

Commit 2cff94cc fixed the shadowed 'link' added by commit 975f0e2e,
but forgot the 'link' added by commit 08aa22ec.

Introduce a common function that will take a callback to resolve links
that will be used to canonicalize paths on various storage systems and
add extensive tests.

The block commit code looks for an explicit base file relative
to the discovered top file; so for a chain of:
  base <- snap1 <- snap2 <- snap3
and a command of:
  virsh blockcommit $dom vda --base snap2 --top snap1
we got a sane message (here from libvirt 1.0.5):
error: invalid argument: could not find base 'snap2' below 'snap1' in chain for 'vda'

Meanwhile, recent refactoring has slightly reduced the quality of the
libvirt error messages, by losing the phrase 'below xyz':
error: invalid argument: could not find image 'snap2' in chain for 'snap3'

But we had a one-off, where we were not excluding the top file
itself in searching for the base; thankfully qemu still reports
the error, but the quality is worse:
  virsh blockcommit $dom vda --base snap2 --top snap2
error: internal error unable to execute QEMU command 'block-commit': Base '/snap2' not found

Fix the one-off in blockcommit by changing the semantics of name
lookup - if a starting point is specified, then the result must
be below that point, rather than including that point.  The only
other call to chain lookup was blockpull code, which was already
forcing the lookup to omit the active layer and only needs a
tweak to use the new semantics.

This also fixes the bug exposed in the testsuite, where when doing
a lookup pinned to an intermediate point in the chain, we were
unable to return the name of the parent also in the chain.

* src/util/virstoragefile.c (virStorageFileChainLookup): Change
semantics for non-NULL startFrom.
* src/qemu/qemu_driver.c (qemuDomainBlockJobImpl): Adjust caller,
to keep existing semantics.
* tests/virstoragetest.c (mymain): Adjust to expose new semantics.
Signed-off-by: NEric Blake <eblake@redhat.com>

Add some more tests of what happens when we restrict a lookup
to begin at a point in the middle of a chain.  In particular,
we want to ensure that a parent is not found when starting at
the child.  This commit also demonstrates that we have a slight
difference in behavior on what parent we report when filtering
is in effect; as the determination of the parent affects the
code in block commit, exposing this in the testsuite will help
justify changes in future patches that tweak the semantics of
what lookups are allowed.

* tests/virstoragetest.c (testStorageLookup): Test user input.
(TEST_LOOKUP_TARGET): Add parameter.
(mymain): Add lookup tests.
Signed-off-by: NEric Blake <eblake@redhat.com>

The next patch will be adding tests, including adding a parameter
for testing more conditions.  For ease of review of that patch, I
want to create common context lines that don't change when the new
tests are added (it's easier to visually review additions than it
is to review an entire chunk of tests rewritten into another
larger chunk of tests).

* tests/virstoragetest.c (mymain): Add a parameter and renumber
the lookup tests.
Signed-off-by: NEric Blake <eblake@redhat.com>

Typing chain->backingStore->backingStore gets old after a while;
introduce some alias variables to make the test more compact.

* tests/virstoragetest.c (mymain): Introduce some shorthand.
Signed-off-by: NEric Blake <eblake@redhat.com>

When the test is failing but the debug output isn't enabled the
resulting line would look ugly like and would not contain the actual
difference.

TEST: virstoragetest
      .................chain member 1!chain member 1!chain member 1!

Store the member index in the actual checked string to hide this problem

All the fields crammed into two lines weren't easy to parse by human
eyes. Split up the format string into lines and put it into a central
variable so that changes in two places aren't necessary.

Use the new backing store parser in the backing chain crawler. This
change needs one test change where information about the NBD image are
now parsed differently.

Stat the path of the storage file being tested to set the correct type
into the virStorageSource. This will avoid breaking the test suite when
inquiring metadata of directory paths in the next patches.

My future work will modify the metadata crawler function to use the
storage driver file APIs to access the files instead of accessing them
directly so that we will be able to request the metadata for remote
files too. To avoid linking the storage driver to every helper file
using the utils code, the backing chain traversal function needs to be
moved to the storage driver source.

Additionally the virt-aa-helper and virstoragetest programs need to be
linked with the storage driver as a result of this change.

In "src/util/" there are many enumeration (enum) declarations.
Sometimes, it's better using a typedef for variable types,
function types and other usages. Other enumeration will be
changed to typedef's in the future.
Signed-off-by: NJulio Faracco <jcfaracco@gmail.com>
Signed-off-by: NEric Blake <eblake@redhat.com>

Each backing store of a given disk is associated with a unique index
(which is also formatted in domain XML) for easier addressing of any
particular backing store. With this patch, any backing store can be
addressed by its disk target and the index. For example, "vdc[4]"
addresses the backing store with index equal to 4 of the disk identified
by "vdc" target. Such shorthand can be used in any API in place for a
backing file path:

    virsh blockcommit domain vda --base vda[3] --top vda[2]
Signed-off-by: NJiri Denemark <jdenemar@redhat.com>

Returning both virStorageSourcePtr and its path member does not make a
lot of sense.
Signed-off-by: NJiri Denemark <jdenemar@redhat.com>

To avoid having the root of a backing chain present twice in the list we
need to invert the working of virStorageFileGetMetadataRecurse.

Until now the recursive worker created a new backing chain element from
the name and other information passed as arguments. This required us to
pass the data of the parent in a deconstructed way and the worker
created a new entry for the parent.

This patch converts this function so that it just fills in metadata
about the parent and creates a backing chain element from those. This
removes the duplication of the first element.

To avoid breaking the test suite, virstoragetest now calls a wrapper
that creates the parent structure explicitly and pre-fills it with the
test data with same function signature as previously used.

Don't remove detected metadata about directory based storage volumes.

To conform with the naming of the planned XML output rename the metadata
variable name.

s/backingMeta/backingStore/g

Replace the old structure with the new one. This change is a trivial
name change operation (along with change of the freeing function).

Remove the obsolete field replaced by data in "path".

The testsuite requires tweaking as the name of the backing file is now
stored one layer deeper in the backing chain linked list.

As for the previous patch, this change is needed to achieve
compatibility with all the existing code, where we expect a fully
qualified path of local files to be present.

To allow future change of virStorageFileMetadata to virStorageSource we
need to store a full path in the "path" variable as rest of the code
expects it to be a full path. Rename the "path" field to "relPath" to
keep tracking the info but allowing a real "path" field.

Another field no longer needed, getting us one step closer to
merging virStorageFileMetadata and virStorageSource.

* src/util/virstoragefile.h (_virStorageFileMetadata): Drop
field.
* src/util/virstoragefile.c (virStorageFileGetMetadataInternal)
(virStorageFileGetMetadataFromFDInternal): Alter signature.
(virStorageFileFreeMetadata, virStorageFileGetMetadataFromBuf)
(virStorageFileGetMetadataFromFD): Adjust clients.
* tests/virstoragetest.c (_testFileData, testStorageChain)
(mymain): Simplify test.
Signed-off-by: NEric Blake <eblake@redhat.com>

Thanks to the testsuite, I feel quite confident that this rewrite
is correct; it gives the same results for all cases except for one.
I can make the argument that _that_ case was a pre-existing bug:
when looking up relative names, the lookup is supposed to be
pegged to the directory that contains the parent qcow2 file.  Thus,
this resolves the fixme first mentioned in commit 367cd69d (even
though I accidentally removed the fixme comment early in 74430fe3).

* src/util/virstoragefile.c (virStorageFileChainLookup): Depend on
new rather than old fields.
* tests/virstoragetest.c (mymain): Adjust test to match fix.
Signed-off-by: NEric Blake <eblake@redhat.com>

The original chain lookup code had to pass in the starting name,
because it was not available in the chain.  But now that we have
added fields to the struct, this parameter is redundant.

* src/util/virstoragefile.h (virStorageFileChainLookup): Alter
signature.
* src/util/virstoragefile.c (virStorageFileChainLookup): Adjust
handling of top of chain.
* src/qemu/qemu_driver.c (qemuDomainBlockCommit): Adjust caller.
* tests/virstoragetest.c (testStorageLookup, mymain): Likewise.
Signed-off-by: NEric Blake <eblake@redhat.com>

I realized that we had no good test coverage of looking up a
name from within a backing chain, even though code like
block-commit is relying on it.

* tests/virstoragetest.c (testStorageLookup): New function.
(mymain): New tests.
Signed-off-by: NEric Blake <eblake@redhat.com>

Drop another redundant field from virStorageFileMetadata.

* src/util/virstoragefile.h (_virStorageFileMetadata): Drop
field.
* src/util/virstoragefile.c
(virStorageFileGetMetadataFromFDInternal)
(virStorageFileGetMetadataFromFD)
(virStorageFileGetMetadataRecurse): Adjust callers.
* tests/virstoragetest.c (_testFileData, testStorageChain)
(mymain): Simplify test.
Signed-off-by: NEric Blake <eblake@redhat.com>

Finally starting to prune away some of the old fields that have
been made redundant by the new fields, on my way towards directly
reusing virStorageSource.

* src/util/virstoragefile.h (_virStorageFileMetadata): Drop
field.
* src/util/virstoragefile.c (virStorageFileGetMetadataInternal)
(virStorageFileChainLookup): Adjust callers.
* tests/virstoragetest.c (_testFileData, testStorageChain)
(mymain): Simplify test.
Signed-off-by: NEric Blake <eblake@redhat.com>

So far, my work has been merely preserving the status quo of
backing file analysis.  But this patch starts to tread in the
territory of making the backing chain code more powerful - we
will eventually support network storage containing non-raw
formats.  Here, we expose metadata information about a network
backing store, even if that information is still hardcoded to
a raw format for now.

* src/util/virstoragefile.c (virStorageFileGetMetadataRecurse):
Also populate struct for non-file backing.
(virStorageFileGetMetadata, virStorageFileGetMetadatainternal):
Recognize non-file top image.
(virFindBackingFile): Add comment.
(virStorageFileChainGetBroken): Adjust comment, ensure output
is set.
* tests/virstoragetest.c (mymain): Update test to reflect it.
Signed-off-by: NEric Blake <eblake@redhat.com>

I'm tired of alternating between test failures due to bugs in
my refactoring work, vs. test failures due to leftovers in
the file system from the previous test.  This patch has no
impact when the testsuite is successful, but doeesn't hurt either.

* tests/virstoragetest.c (testPrepImages): Clean up from prior
failed test.
Signed-off-by: NEric Blake <eblake@redhat.com>

Validate that all the new fields are getting set to desired values.

* tests/virstoragetest.c (_testFileData, testStorageChain): Check
for more fields.
(mymain): Populate additional fields.
Signed-off-by: NEric Blake <eblake@redhat.com>

The testsuite is absolutely essential to feeling comfortable
about swapping the backing chain structure over to a new format.
This patch tests the path settings, and demonstrates that the
correct short name is being passed to the child.

* tests/virstoragetest.c (testStorageChain): Test path.
(mymain): Update expected data.
Signed-off-by: NEric Blake <eblake@redhat.com>

A later patch will be adding some new fields to
virStorageFileMetadata; to minimize confusion, renaming the
test fields now will make it more obvious which fields are
being tested later.

* tests/virstoragetest.c (_testFileData): Alter names.
(testStorageChain, mymain): Adjust clients.
Signed-off-by: NEric Blake <eblake@redhat.com>

Introduced in commit d1e55de3.
virstoragetest.c: In function ‘testStorageChain’:
virstoragetest.c:249:10: warning: declaration of ‘abs’ shadows a global
declaration [-Wshadow]

Another reduction in the number of structs I have to modify
when I start tracking new fields in virStorageFileMetadata.

* tests/virstoragetest.c (_testFileData): Add fields.
(testStorageChain): Select between fields based on flag.
(mymain): Record both absolute and relative expectations in one
struct.
Signed-off-by: NEric Blake <eblake@redhat.com>

As I add more tests, it's getting harder to follow the split between
a struct in one place and a test using the struct in another.
Interleaving the tests makes changes more localized, and also makes
debugging easier when a test goes wrong during my refactoring work.

* tests/virstoragetest.c (mymain): Modify structs as we go, rather
than up-front.
(testStorageChain): Make failure debugging easier.
Signed-off-by: NEric Blake <eblake@redhat.com>

Part of the upcoming refactoring will change how broken chains
are detected; it makes sense to test that this works.  In
particular, test the just-fixed infinite loop detection bug.
Also, make sure that detection of directories is sane.

* tests/virstoragetest.c (testStorageChain): Enhance test.
(mymain): Add more tests.
(testCleanupImages, testPrepImages): Populate a directory.
Signed-off-by: NEric Blake <eblake@redhat.com>

I'm about to add fields to virStorageFileMetadata, which means
also adding fields to the testFileData struct in virstoragetest.
Alas, adding even one pointer on an x86_64 machine gave me a
dreaded compiler error:

virstoragetest.c:712:1: error: the frame size of 4208 bytes is larger than 4096 bytes [-Werror=frame-larger-than=]

After some experimentation, I realized that each test was creating
yet another testChainData (which contains testFileData) on the stack;
forcing the reuse of one of these structures instead of creating a
fresh one each time drastically reduces the size requirements.  While
at it, I also got rid of a lot of intermediate structs, with some
macro magic that lets me directly build up the destination chains
inline.

For a bit more insight into what this patch does:
The old code uses an intermediate variable as a fixed-size array
of structs:
testFileData chain[] = { a, b };
data.files = chain;

In the new code, the use of VIR_FLATTEN_* allows the TEST_CHAIN()
macro to still take a single argument for each chain, but now of
the form '(a, b)', where it is turned into the var-args 'a, b'
multiple arguments understood by TEST_ONE_CHAIN().  Thus, the
new code avoids an intermediate variable, and directly provides
the list of pointers to be assigned into array elements:
data.files = { &a, &b };

* tests/virstoragetest.c (mymain): Rewrite TEST_ONE_CHAIN to
reuse the same struct for each test, and to take the data
inline rather than via intermediate variables.
(testChainData): Use bounded array of pointers instead of
unlimited array of struct.
(testStorageChain): Reflect struct change.
Signed-off-by: NEric Blake <eblake@redhat.com>

Writing this test with C99 initializers will make it easier to test
additions and deletions to struct members as I refactor the code.

* tests/virstoragetest.c (mymain): Rewrite initializers.
Signed-off-by: NEric Blake <eblake@redhat.com>

No need to spawn a child 'rm' process when we can do it ourselves.

* tests/virstoragetest.c (testCleanupImages): Use dedicated
helper.
Signed-off-by: NEric Blake <eblake@redhat.com>