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Date: Thu, 16 Jul 2009 17:11:21 +0200
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
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Subject: Re: MVFS results
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On Jul 16 13:58, Eric Blake wrote:
> Corinna Vinschen <corinna-cygwin <at> cygwin.com> writes:
> > For instance, maybe it chokes on the sharing flags.  I'd try with
> > FILE_SHARE_VALID_FLAGS instead of just FILE_SHARE_DELETE.
> > 
> > Btw., it's very helpful to observe what happens exactly using
> > sysinternal's procmon.
> 
> What would you like to see?  Here's a few procman entries captured immediately 

I can't make a lot out of the output without the chance to try
what's going on when changing the arguments.  In the first place
I mentioned it for your convenience.  But let's see...

> [...]
> 7:39:53.9322032 AM	rm.exe	5912	QueryAllInformationFile
> 	G:\views\fabt_eblake.vws\.s\00049\800039b14a4a8b07foo	BUFFER OVERFLOW
> 	CreationTime: 7/15/2009 3:42:16 PM, LastAccessTime: 7/15/2009 3:42:16 
> PM, LastWriteTime: 7/15/2009 3:42:16 PM, ChangeTime: 7/15/2009 3:42:16 PM, 
> FileAttributes: RA, AllocationSize: 0, EndOfFile: 0, NumberOfLinks: 1, 
> DeletePending: False, Directory: False, IndexNumber: 0x47283402d42464, EaSize: 
> 0, Access: None, Position: 0, Mode: , AlignmentRequirement: Byte
> 
> 7:40:37.3023584 AM	rm.exe	5912	CreateFile
> 	M:\u_fabt_eblake\FABT_Development\FABT_MPG_Process_BSP_SPCI\foo	ACCESS 
> DENIED	Desired Access: Generic Write, Delete, Disposition: Open, Options: Open 
> For Backup, Attributes: n/a, ShareMode: Delete, AllocationSize: n/a

Yeah, ACCESS DENIED, but why?

> Next, I'll have to play with your advice to play with the various ShareMode 
> flags.

Yes, that's a chance.

Another idea would be that the MVFS driver refuses the open request for
DELETE *because* the R/O flag is set.  That's wrong behaviour but it is
as it is.  If I'm right, you would have to open the file with
FILE_WRITE_ATTRIBUTES permission only, remove the R/O flag, re-open the
file with DELETE access, close the original handle, and then go ahead
with the default unlink procedure, along these lines (tested on FAT):

Index: syscalls.cc
===================================================================
RCS file: /cvs/src/src/winsup/cygwin/syscalls.cc,v
retrieving revision 1.521
diff -u -p -r1.521 syscalls.cc
--- syscalls.cc	14 Jul 2009 17:37:42 -0000	1.521
+++ syscalls.cc	16 Jul 2009 15:09:25 -0000
@@ -445,17 +445,13 @@ NTSTATUS
 unlink_nt (path_conv &pc)
 {
   NTSTATUS status;
-  HANDLE fh;
+  HANDLE fh, fh_ro = NULL;
   OBJECT_ATTRIBUTES attr;
   IO_STATUS_BLOCK io;
 
-  ACCESS_MASK access = DELETE;
-  /* If the R/O attribute is set, we have to open the file with
-     FILE_WRITE_ATTRIBUTES to be able to remove this flags before trying
-     to delete it. */
-  if (pc.file_attributes () & FILE_ATTRIBUTE_READONLY)
-    access |= FILE_WRITE_ATTRIBUTES;
+  bin_status bin_stat = dont_move;
 
+  ACCESS_MASK access = DELETE;
   ULONG flags = FILE_OPEN_FOR_BACKUP_INTENT;
   /* Add the reparse point flag to native symlinks, otherwise we remove the
      target, not the symlink. */
@@ -463,13 +459,29 @@ unlink_nt (path_conv &pc)
     flags |= FILE_OPEN_REPARSE_POINT;
 
   pc.get_object_attr (attr, sec_none_nih);
+  /* If the R/O attribute is set, we have to open the file with
+     FILE_WRITE_ATTRIBUTES to be able to remove this flags before trying
+     to delete it. */
+  if (pc.file_attributes () & FILE_ATTRIBUTE_READONLY)
+    {
+      access |= FILE_WRITE_ATTRIBUTES;
+      status = NtOpenFile (&fh_ro, FILE_WRITE_ATTRIBUTES, &attr, &io,
+			   FILE_SHARE_VALID_FLAGS, flags);
+      if (NT_SUCCESS (status))
+	{
+	  NtSetAttributesFile (fh_ro, pc.file_attributes ()
+				      & ~FILE_ATTRIBUTE_READONLY);
+	  InitializeObjectAttributes (&attr, &ro_u_empty,
+				      pc.objcaseinsensitive (), fh_ro, NULL);
+      	}
+    }
+
   /* First try to open the file with only allowing sharing for delete.  If
      the file has an open handle on it, other than just for deletion, this
      will fail.  That indicates that the file has to be moved to the recycle
      bin so that it actually disappears from its directory even though its
      in use.  Otherwise, if opening doesn't fail, the file is not in use and
      we can go straight to setting the delete disposition flag. */
-  bin_status bin_stat = dont_move;
   status = NtOpenFile (&fh, access, &attr, &io, FILE_SHARE_DELETE, flags);
   if (status == STATUS_SHARING_VIOLATION || status == STATUS_LOCK_NOT_GRANTED)
     {
@@ -512,11 +524,15 @@ unlink_nt (path_conv &pc)
 	      if (!NT_SUCCESS (status))
 		{
 		  NtClose (fh);
+		  if (fh_ro)
+		    NtClose (fh_ro);
 		  return status;
 		}
 	    }
 	}
     }
+  if (fh_ro)
+    NtClose (fh_ro);
   if (!NT_SUCCESS (status))
     {
       if (status == STATUS_DELETE_PENDING)
@@ -527,9 +543,6 @@ unlink_nt (path_conv &pc)
       syscall_printf ("Opening file for delete failed, status = %p", status);
       return status;
     }
-  /* Get rid of read-only attribute. */
-  if (access & FILE_WRITE_ATTRIBUTES)
-    NtSetAttributesFile (fh, pc.file_attributes () & ~FILE_ATTRIBUTE_READONLY);
   /* Try to move to bin if a sharing violation occured.  If that worked,
      we're done. */
   if (bin_stat == move_to_bin


> [*] This was my first time using procmon - cool tool!

Indeed!  It was very helpful to figure out how the MSFT NFS client
works.


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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