Re: Possible problem with zero-copy TCP and sendfile()

[Jan Kasprzak <kas@informatics.muni.cz>]

Jesse S Sipprell wrote:
: After cursory examination of proftpd, it appears that there is a misuse of the
: sendfile() call under Linux, which may be responsible for the corruption.  The
: code was originally based on BSD semantics.  Under Linux, the offset argument
: is not being used correctly to determine how much data has been sent in the
: case of EINTR.
: 
: A patch will be coming out soon, as it is a fairly trivial fix.
: 
	FWIW, I've fixed ProFTPd on my server with the following patch.
Sorry for making noise @ linux-kernel list, it was totally unrelated
to the Linux kernel:

--- proftpd-1.2.2rc1/src/data.c.sendfile	Thu Feb 15 15:24:53 2001
+++ proftpd-1.2.2rc1/src/data.c	Tue Apr 17 21:35:24 2001
@@ -760,7 +760,9 @@
      *
      * ssize_t sendfile(int out_fd, int in_fd, off_t *offset, size_t count)
      */
-    if((len = sendfile(session.d->outf->fd, retr_fd, offset, count)) == -1) {
+    len = sendfile(session.d->outf->fd, retr_fd, offset, count);
+    if (len == -1 || len > 0 && len < count) {
+       errno = EINTR;
 #elif defined(HAVE_BSD_SENDFILE)
     /* BSD semantics for sendfile are flexible...it'd be nice if we could
      * standardize on something like it.  The semantics are:
@@ -797,7 +799,9 @@
 	if((count -= len) <= 0)
 	  break;
 	
+#if !defined(HAVE_LINUX_SENDFILE)
 	*offset += len;
+#endif
 	
 	if(TimeoutStalled)
 	  reset_timer(TIMER_STALLED, ANY_MODULE);

-Yenya

-- 
\ Jan "Yenya" Kasprzak <kas at fi.muni.cz>       http://www.fi.muni.cz/~kas/
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