Current Samba master incorrectly returns STATUS_INVALID_HANDLE on copy_chunk

[Ralph Boehme]

On 11/9/24 4:26 PM, Ralph Boehme via samba-technical wrote:
> On 10/9/24 9:43 PM, Jeremy Allison wrote:
>> Can we just map (access_mask (FILE_APPEND_DATA|SYNCHRONIZE)) == 
>> (FILE_APPEND_DATA|SYNCHRONIZE))
>> to O_APPEND, regardless of POSIX mode ?
> 
> thinking about this a bit more, this seems doable, albeit only for POSIX 
> mode. For non-POSIX mode we could potentially break WIndows application 
> that open only with FILE_APPEND_DATA: I checked with a torture test that 
> Windows doesn't enforce append behaviour for FILE_APPEND_DATA|SYNCHRONIZE.
> 
> For POSIX opens we should also allow combinations like 
> FILE_READ_ATTRIBUTES|FILE_APPEND_DATA to map to O_APPEND, so clients can 
> write in append mode to the handle and still are able to fstat() it.
> 
> https://gitlab.com/samba-team/samba/-/merge_requests/3863

in addition, I guess for SMB3 POSIX we might want to require that the 
client sets offset=-2 in SMB2-WRITES on a handle opened with append 
semantics, reusing the logic from MS-FSA.

This avoids bringing in the ambiguity of POSIX vs Linux pwrite() 
O_APPEND behaviour into the protocol by clearly specifying: if a handle 
is opened in append mode, all writes are using write() with O_APPEND 
semantics which are clearly specified.

Looking at possible server implementations, it seems both Linux and 
FreeBSD note in man pwrite() under BUGS, that a pwrite() on a handle 
opened with O_APPEND ignores the offset, so we in Samba we can continue 
to use pwrite() in SMB_VFS_PWRITE() default backend.

To avoid relying on BUGS, we can check for and use pwritev2() with 
flags=RWF_APPEND, at least on Linux.

-slow

-------------- next part --------------
A non-text attachment was scrubbed...
Name: OpenPGP_signature.asc
Type: application/pgp-signature
Size: 840 bytes
Desc: OpenPGP digital signature
URL: <http://lists.samba.org/pipermail/samba-technical/attachments/20241109/47142f31/OpenPGP_signature.sig>