Hi,
The return value of ntfs_attr_pwrite() is documented as follows:
> On success, return the number of successfully written bytes. If this number
> is lower than @count this means that an error was encountered during the
> write so that the write is partial. 0 means nothing was written (also return
> 0 when @count is 0).
Hence, a short count implies that an error occurred. However, I discovered that
a short count may, in fact, be returned when successfully writing to a
compressed attribute, since ntfs_attr_pwrite() truncates the count to a single
compression block only:
> if (compressed) {
> fullcount = (pos | (na->compression_block_size - 1)) + 1 - pos;
> if (count > fullcount)
> count = fullcount;
> }
There are two possible ways to fix this:
1) Update ntfs_attr_pwrite() to always try to write the full count
2) Update ntfs_attr_pwrite() documentation to clarify that short returns
are allowed and applications should, generally, continue calling
ntfs_attr_pwrite() until all bytes have been written
It looks like the callers of ntfs_attr_pwrite() in the FUSE drivers do retry
short writes, but this doesn't appear to be the case for all internal callers in
libntfs-3g itself. So I think that option (1) is preferred, if it is at all
possible.
Eric
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