Re: [libvirt] alignment of data fields when compiling with mingwin

I will try these ways, in my search I have also seen some explainations that said to PInvoke char* as IntPtr instead of string in structures, then use Marshal.PtrToStringAnsi/Marshal.StringToHGlobalAnsi but for now it fails. I will try with the strdup PInvoke. -------------------------------------------------- From: "Matthias Bolte" <matthias.bolte(a)googlemail.com&gt; Sent: Sunday, October 17, 2010 6:58 PM To: <arnaud.champion(a)devatom.fr&gt; Cc: <libvir-list(a)redhat.com&gt; Subject: Re: [libvirt] alignment of data fields when compiling with mingwin > A bit of googling turns this function up > > Marshal.StringToHGlobalAnsi > Marshal.StringToHGlobalAuto > Marshal.StringToHGlobalUni > > they create an unmanaged copy a managed string. > > But those might not help, because the docs say that the returned > IntPtr must be freed using Marshal.FreeHGlobal. All this methods use > the GlobalAlloc function from the WinAPI to allocate memory. Maybe > GlobalAlloc is not compatible with the "libc" free function that > libvirt will use to free the memory. > > A bit more googling told me how to import functions from DLLs in C#. > This one imports strdup: > > [DllImport("msvcrt.dll"), CLSCompliant(false)] > public static extern IntPtr _strdup([Const] IntPtr strSource); > > Maybe you can do something like this: > > string result_original = ...; > IntPtr result_global = StringToHGlobalAuto(result_original); > IntPtr result_duplicated = _strdup(result_global); > FreeHGlobal(result_global); > > Then pass result_duplicated to libvirt. > > I'm not sure if that works at all. Maybe there is a simpler/better > solution for this. > > Matthias > > 2010/10/17 <arnaud.champion(a)devatom.fr&gt;: >> You are perfectly right, I have to find the way to avoid C# memory >> freeing ! >> You're a master ;) >> >> Arnaud >> >> -------------------------------------------------- >> From: "Matthias Bolte" <matthias.bolte(a)googlemail.com&gt; >> Sent: Sunday, October 17, 2010 3:21 PM >> To: <arnaud.champion(a)devatom.fr&gt; >> Cc: <libvir-list(a)redhat.com&gt; >> Subject: Re: [libvirt] alignment of data fields when compiling with >> mingwin >> >>> 2010/10/17 <arnaud.champion(a)devatom.fr&gt;: >>>> >>>> Hi Matthias, >>>> >>>> I'm working on the virConnectOpenAuth method C# binding. And in fact, >>>> It >>>> partially work. Let me explain you : >>>> >>> >>> >>>> Now, I have made a little code to connect to an esx hypervisor like >>>> this >>>> : >>>> >>>> ... some init stuff... >>>> >>>> // Define the virConnectAuth struct >>>> virConnectAuth auth = new virConnectAuth >>>> { >>>> cbdata = authDataPtr, >>>> cb = AuthCallback, >>>> credtypes = credtypesPtr, >>>> ncredtype = (uint)credtypes.Length >>>> }; >>>> >>>> IntPtr conn = libVirt.virConnectOpenAuth(tbURI.Text, ref >>>> auth, >>>> 0); >>>> >>>> I have the call back method "AuthCallback" defined like this : >>>> >>>> private int AuthCallback(IntPtr creds, uint ncred, IntPtr cbdata) >>>> { >>>> >>>> AuthData authData = (AuthData) Marshal.PtrToStructure(cbdata, >>>> typeof (AuthData)); >>>> int offset = 0; >>>> int credIndex = 0; >>>> >>>> while (credIndex < ncred) >>>> { >>>> IntPtr currentCred = new IntPtr(creds.ToInt32() + >>>> offset); >>>> >>>> virConnectCredential cred = (virConnectCredential) >>>> Marshal.PtrToStructure(currentCred, typeof (virConnectCredential)); >>>> offset += Marshal.SizeOf(cred); >>>> switch(cred.type) >>>> { >>>> case virConnectCredentialType.VIR_CRED_AUTHNAME: >>>> cred.result = authData.user_name; >>>> cred.resultlen = (uint)authData.user_name.Length; >>>> break; >>>> case virConnectCredentialType.VIR_CRED_PASSPHRASE: >>>> cred.result = authData.password; >>>> cred.resultlen = (uint) authData.password.Length; >>>> break; >>>> default: >>>> return -1; >>>> } >>>> Marshal.StructureToPtr(cred, currentCred, true); >>>> >>>> credIndex++; >>>> } >>>> return 0; >>>> } >>>> >>>> When I test this code, all seems to work well, I mean the >>>> "AuthCallback" >>>> method is called twice, once for authname and once for passphrase. >>>> >>>> But when I run my code in a debugger of Visual Studio I have these >>>> messages >>>> : >>>> >>>> HEAP[Win32_virConnectOpenAuth.exe]: Invalid address specified to >>>> RtlFreeHeap( 00700000, 00EE6D78 ) >>>> HEAP[Win32_virConnectOpenAuth.exe]: Invalid address specified to >>>> RtlFreeHeap( 00700000, 00EE6A80 ) >>>> HEAP[Win32_virConnectOpenAuth.exe]: Invalid address specified to >>>> RtlFreeHeap( 00700000, 00EE6D78 ) >>>> HEAP[Win32_virConnectOpenAuth.exe]: Invalid address specified to >>>> RtlFreeHeap( 00700000, 00EE6A80 ) >>>> HEAP[Win32_virConnectOpenAuth.exe]: Invalid address specified to >>>> RtlFreeHeap( 00EE0000, 007DE480 ) >>>> >>>> but the connection is done, and I am able to list domains of the >>>> hypervisor >>>> for example. The real problem is that this program only work inside >>>> the >>>> the >>>> visual studio debugger, when I launch the executable without debugger, >>>> it >>>> fails. >>>> So I am searching why this doesn't work, I want to check the bindings. >>>> And I >>>> also want to try to fill the "result" member of the >>>> virConnectCredential >>>> structure directly to understanding what can be the problem. >>> >>> >>> Okay, you see an invalid free call either because free is called on an >>> initial invalid pointer of because free is called twice on the same >>> pointer (on the second call the pointer is invalid). >>> >>> When you look at the libvirt codebase in src/util/authhelper.c in >>> virRequestUsername you'll see that the cred.result is returned to the >>> driver directly without making a copy of it. The driver is then >>> responsible for freeing this memory. So the ownership of the memory >>> cred.result points to is transferred from your callback to the driver. >>> >>> I think you see a double-free here because libvirt and C# are both >>> trying to free the same memory, but C# should not do this. I'm not >>> familiar with C#, so I'm just guessing here based on what you have >>> described. This cannot be a problem with the alignment or struct >>> layout, otherwise authentication would not work. >>> >>> You can test if it's double-free by applying the attached patch to >>> libvirt. This patch stops the virRequestUsername and >>> virRequestPassword functions from transferring ownership of the >>> cred.result by copying the string. This creates a memory leak in the >>> normal case, but should stop the double-free in case C# is freeing >>> cred.result here. >>> >>> Matthias >>> >>> >>>> Anyway, thanks ofr these informations, this can help. >>>> >>>> Best regards, >>>> >>>> Arnaud >>>> >>>> -------------------------------------------------- >>>> From: "Matthias Bolte" <matthias.bolte(a)googlemail.com&gt; >>>> Sent: Sunday, October 17, 2010 12:04 PM >>>> To: <arnaud.champion(a)devatom.fr&gt; >>>> Cc: <libvir-list(a)redhat.com&gt; >>>> Subject: Re: [libvirt] alignment of data fields when compiling with >>>> mingwin >>>> >>>>> 2010/10/15 <arnaud.champion(a)devatom.fr&gt;: >>>>>> >>>>>> Hi, >>>>>> >>>>>> I'm currently working on libvirt csharp bindings, and I have some >>>>>> trouble >>>>>> with virConnectOpenAuth marshaling. >>>>>> I need to know what is the alignment of data fields in structure >>>>>> when >>>>>> compiling with mingwin. >>>>>> Anyone know that ? >>>>>> >>>>>> cheers, >>>>>> >>>>>> Arnaud Champion >>>>>> >>>>> >>>>> Why do you need to know the alignment? Do you need to build or access >>>>> members of the virConnectCredential or virConnectAuth structs by >>>>> offset in memory? >>>>> >>>>> The Wikipedia article about data structure alignment might be helpful >>>>> when you really need to care about alignment. >>>>> >>>>> If you actually need the offset of the members in those structs you >>>>> can just use the offsetof macro and let the compiler tell you: >>>>> >>>>> #include <stdio.h> >>>>> #include <stddef.h> >>>>> #include <libvirt/libvirt.h> >>>>> >>>>> void main(void) >>>>> { >>>>> printf("virConnectCredential\n"); >>>>> printf(" type %2u\n", offsetof(virConnectCredential, type)); >>>>> printf(" prompt %2u\n", offsetof(virConnectCredential, prompt)); >>>>> printf(" challenge %2u\n", offsetof(virConnectCredential, >>>>> challenge)); >>>>> printf(" defresult %2u\n", offsetof(virConnectCredential, >>>>> defresult)); >>>>> printf(" result %2u\n", offsetof(virConnectCredential, result)); >>>>> printf(" resultlen %2u\n", offsetof(virConnectCredential, >>>>> resultlen)); >>>>> printf("\n"); >>>>> printf("virConnectAuth\n"); >>>>> printf(" credtype %2u\n", offsetof(virConnectAuth, credtype)); >>>>> printf(" ncredtype %2u\n", offsetof(virConnectAuth, ncredtype)); >>>>> printf(" cb %2u\n", offsetof(virConnectAuth, cb)); >>>>> printf(" cbdata %2u\n", offsetof(virConnectAuth, cbdata)); >>>>> } >>>>> >>>>> >>>>> Output on x86: >>>>> >>>>> virConnectCredential >>>>> type 0 >>>>> prompt 4 >>>>> challenge 8 >>>>> defresult 12 >>>>> result 16 >>>>> resultlen 20 >>>>> >>>>> virConnectAuth >>>>> credtype 0 >>>>> ncredtype 4 >>>>> cb 8 >>>>> cbdata 12 >>>>> >>>>> >>>>> Output on x86_64: >>>>> >>>>> virConnectCredential >>>>> type 0 >>>>> prompt 8 >>>>> challenge 16 >>>>> defresult 24 >>>>> result 32 >>>>> resultlen 40 >>>>> >>>>> virConnectAuth >>>>> credtype 0 >>>>> ncredtype 8 >>>>> cb 16 >>>>> cbdata 24 >>>>> >>>>> [1] >>>>> >>>>> http://en.wikipedia.org/wiki/Data_structure_alignment#Typical_alignment_o... >>>>> >>>>> Matthias >>>> >>>> >>>> >>> >> >> > -- libvir-list mailing list libvir-list(a)redhat.com https://www.redhat.com/mailman/listinfo/libvir-list