Commit e0c469e58b93f852a72265919703cb6abd3779f8 that fixes the detection of image chain wasn't complete. Iteration through the backing image chain has to stop at the last existing image if some of the images are missing otherwise the backing chain that is cached contains entries with paths being set to NULL resulting to: error: Unable to allow access for disk path (null): Bad address Fortunately stat() is kind enough not to crash when it's presented with a NULL argument.

--- src/util/storage_file.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/src/util/storage_file.c b/src/util/storage_file.c index 2249212..e7cbea7 100644 --- a/src/util/storage_file.c +++ b/src/util/storage_file.c @@ -729,6 +729,8 @@ virStorageFileGetMetadataFromBuf(int format, if (meta->backingStore == NULL) { /* the backing file is (currently) unavailable, treat this * file as standalone */ + VIR_FREE(meta->backingStoreRaw); + meta->backingStoreIsFile = false; backingFormat = VIR_STORAGE_FILE_NONE;

On 11/21/2012 04:05 AM, Peter Krempa wrote: > Commit e0c469e58b93f852a72265919703cb6abd3779f8 that fixes the detection > of image chain wasn't complete. Iteration through the backing image > chain has to stop at the last existing image if some of the images are > missing otherwise the backing chain that is cached contains entries with > paths being set to NULL resulting to: > > error: Unable to allow access for disk path (null): Bad address > > Fortunately stat() is kind enough not to crash when it's presented with > a NULL argument. That's only true for stat() on Linux; other OSs are fully entitled to crash, so this definitely needs fixing :) > --- > src/util/storage_file.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/src/util/storage_file.c b/src/util/storage_file.c > index 2249212..e7cbea7 100644 > --- a/src/util/storage_file.c > +++ b/src/util/storage_file.c > @@ -729,6 +729,8 @@ virStorageFileGetMetadataFromBuf(int format, > if (meta->backingStore == NULL) { > /* the backing file is (currently) unavailable, treat this > * file as standalone */ > + VIR_FREE(meta->backingStoreRaw);

> + meta->backingStoreIsFile = false;

> backingFormat = VIR_STORAGE_FILE_NONE; Hmm, I'm wondering if this is the right place to fix it, or if we are throwing away information too early. That is, are we sure it is not the later client of the chain at fault for not recognizing VIR_STORAGE_FILE_NONE coupled with non-NULL backingStoreRaw as the key for whether a backing file is missing? I'm guessing domain_conf.c:virDomainDiskDefForeachPath would be the real function to fix here.

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On 11/22/2012 04:26 AM, Peter Krempa wrote: >>> +++ b/src/util/storage_file.c >>> @@ -729,6 +729,8 @@ virStorageFileGetMetadataFromBuf(int format, >>> if (meta->backingStore == NULL) { >>> /* the backing file is (currently) unavailable, >>> treat this >>> * file as standalone */ >>> + VIR_FREE(meta->backingStoreRaw); > > Also I should explain the following thing: > > This freeing of meta->backingStoreRaw actualy doesn't fix the bug. It > just felt a right thing to do when the backing file is missing. Hmm, actually, keeping this around might be nice if someone inspecting the chain for missing backing files wants to know that the file was missing. But if the same information is also found in meta->backingStore, then I guess freeing it is okay (that is, the idea is that for a missing backing file, we should be leaving enough breadcrumbs for later clients to diagnose what is missing, but also to know that it is missing).

> >>> + meta->backingStoreIsFile = false; > > This line is the actual fix. The code that recursively detects the image > chain uses this value as a marker if another iteration of the recursion > is needed (on the non-existing file). Ah - this line indeed makes sense, then. If we are going to set the format as NONE, then we should also mark that it is not a regular file (it is a missing file). Keep this change. > > >>> backingFormat = VIR_STORAGE_FILE_NONE; >> >> Hmm, I'm wondering if this is the right place to fix it, or if we are >> throwing away information too early. That is, are we sure it is not the >> later client of the chain at fault for not recognizing >> VIR_STORAGE_FILE_NONE coupled with non-NULL backingStoreRaw as the key >> for whether a backing file is missing? I'm guessing >> domain_conf.c:virDomainDiskDefForeachPath would be the real function to >> fix here. > > I will add the check also here, but I'd like to discuss the creating of > the chain in the first place. So it sounds like the real fix needs to touch both places - the creation of the chain to make sure it leaves enough breadcrumbs, and the iteration over the chain to make sure that it handles a missing backing file according to the user's wishes (since virDomainDiskDefForeachPath has bool ignoreOpenFailure that says whether to ignore a missing file or to fail because the chain is incomplete). I knew this area of code would be tricky when I first started touching it :(