Hi Christoph, On Sun, Jan 10, 2010 at 3:49 AM, Christoph Hellwig <hch@xxxxxx> wrote: > Are you going to put this or some equivalent note in? Currently the > manpages is extremly dangerous as it doesn't warn people about this > system call not actually guaranteeing any data integrity. I lightly edited your patch, and applied it. Sorry for the long delay. Cheers, Michael > On Thu, Aug 27, 2009 at 08:01:16PM +0200, Christoph Hellwig 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 > ---end quoted text--- > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Author of "The Linux Programming Interface" 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
