These days, I’m studying pnfs’ functionalities. It seems that the pnfs code does not support direct I/O. Actually, in direct IO mode, the generic_file_aio_read() is not called. Is there a plan to support direct IO in pnfs? And in nfs_file_direct_read() comment, what’s meaning of the sentence(in order to avoid gfar’s check ~ end of file)? /** * nfs_file_direct_read - file direct read operation for NFS files * @iocb: target I/O control block * @iov: vector of user buffers into which to read data * @nr_segs: size of iov vector * @pos: byte offset in file where reading starts * * We use this function for direct reads instead of calling * generic_file_aio_read() in order to avoid gfar's check to see if * the request starts before the end of the file. For that check * to work, we must generate a GETATTR before each direct read, and * even then there is a window between the GETATTR and the subsequent * READ where the file size could change. Our preference is simply * to do all reads the application wants, and the server will take * care of managing the end of file boundary. * * This function also eliminates unnecessarily updating the file's * atime locally, as the NFS server sets the file's atime, and this * client must read the updated atime from the server back into its * cache. */ --------------------------------------------------------------------- SOO-YOUNG KIM Senior Member of Engineering Staff Storage System Research Team Electronics and Telecommunications Research Institute 138 Gajeong-no, Yuseong-gu, Daejeon, 305-700 KOREA Phone : 82-42-860-1682 Fax : 82-42-860-6699 Mobile : 82-10-9696-3032 E-mail : sykim@xxxxxxxxxx ETRI Homepage : www.etri.re.kr --------------------------------------------------------------------- -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
