bin/89100: premature EOF with ftpd on some large files

[Deomid Ryabkov]

The following reply was made to PR bin/89100; it has been noted by GNATS.

From: Deomid Ryabkov <myself at rojer.pp.ru>
To: bug-followup at FreeBSD.org, dkelly at hiwaay.net
Cc:  
Subject: Re: bin/89100: premature EOF with ftpd on some large files
Date: Mon, 05 Dec 2005 23:44:05 +0300

 i have similar problem: sendfile(2) returns prematurely,
 when exactly 2^32 bytes left to transfer.
 this is demonstrated by ftpd (which uses sendfile), but applies to
 apache too (if configured with enablesendfile yes).
 in my case, sendfile misbehaves only when asked to send file residing on
 NFS-mounted filesystem.
 this seems to happen to all files > 4G resiging on NFS-mounted
 filesystems. those same files can be read without problem with read(2),
 therefore copying with cp(1) succeeds.
 
 while tracking down the problem i set up a local ftp server on my
 notebook, rooted at /stuff/ftp.
 i was able to download a large file residing on local hard disk without
 problem:
 
 nb[/stuff/ftp]# fetch -o /dev/null
 ftp://192.168.10.4/debian-31r0a-i386-binary-1.iso
 /dev/null                                     100% of 4469 MB   14 MBps
 00m00s
 
 then i tried downloading the same file from NFS-mounted filesystem:
 
 nb[/stuff/ftp]# mount
 <snip>
 tux:/spool on /stuff/ftp/spool (nfs)
 nb[/stuff/ftp]# fetch -o /dev/null
 ftp://192.168.10.4/spool/distr/debian-31r0a-i386-binary-1.iso
 /dev/null                                       8% of 4469 MB 7310 kBps
 09m30s
 fetch: /dev/null appears to be truncated: 391739392/4686706688 bytes
 
 and another one:
 
 nb[/stuff/ftp]# fetch -o /dev/null
 ftp://192.168.10.4/spool/distr/debian-31r0a-i386-binary-2.iso
 /dev/null                                       3% of 4223 MB 7367 kBps
 09m37s
 fetch: /dev/null appears to be truncated: 133883904/4428851200 bytes
 
 in both cases, transfer ends at exactly 4294967296=2^32 bytes before
 actual end of file.
 one line of debug output added to ftpd.c shows that sendfile actually
 returns without error, with correct amount of transferred bytes:
 
 Dec  5 23:34:26 nb ftpd[55338]: sendfile returned 0, errno=2,
 cnt=391739392
 Dec  5 23:39:21 nb ftpd[55352]: sendfile returned 0, errno=2,
 cnt=133883904