Hi Christoph, Thanks for this patch. Since Andrew was the original author of this syscall, I'd like him to take a look at these changes, to get some review. Andrew? Thanks Michael On Thu, Aug 27, 2009 at 8:01 PM, Christoph Hellwig <hch@xxxxxx> wrote: > This system call is by design completely unsuitable for any data > integrity operations. Make that very clear in the manpage. > > > Signed-off-by: Christoph Hellwig <hch@xxxxxx> > > Index: man-pages/man2/sync_file_range.2 > =================================================================== > --- man-pages.orig/man2/sync_file_range.2 2009-08-27 14:51:51.373360594 -0300 > +++ man-pages/man2/sync_file_range.2 2009-08-27 14:57:35.213854927 -0300 > @@ -80,11 +80,22 @@ after performing any write. > Specifying > .I flags > as 0 is permitted, as a no-op. > -.SS Some details > -None of these operations write out the file's metadata. > +.SS WARNING > +This system call is extremly dangerous and should not be used in portable > +programs. None of these operations write out the file's metadata. > Therefore, unless the application is strictly performing overwrites of > -already-instantiated disk blocks, > -there are no guarantees that the data will be available after a crash. > +already-instantiated disk blocks, there are no guarantees that the data will > +be available after a crash. There is no user interface to know if a > +write is purely an overwrite. On filesystem using copy on write semantics > +like > +.IR btrfs > +an over write of existing allocated blocks is impossible. Writing into > +pre-allocated space many filesystems also require calls into the block > +allocator which this system call does not sync out to disk. > +This system call does not flush disk write caches and thus does not provide > +any data integrity on systems with volatile disk write caches. > + > +.SS Some details > > .B SYNC_FILE_RANGE_WAIT_BEFORE > and > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Watch my Linux system programming book progress to publication! http://blog.man7.org/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
