https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=207092
Bug ID: 207092
Summary: dd conv=sparse is broken since r265593
Product: Base System
Version: 10.2-STABLE
Hardware: Any
OS: Any
Status: New
Severity: Affects Many People
Priority: ---
Component: bin
Assignee: freebsd-bugs@FreeBSD.org
Reporter: sobo...@freebsd.org
The dd(1) sparse conversion is seriously broken after this change. The last
block is never written at least for the case of output being regular file:
$ dd if=/dev/zero of=/tmp/foo.bar bs=1m count=10
10+0 records in
10+0 records out
10485760 bytes transferred in 0.003244 secs (3232431656 bytes/sec)
$ ktrace dd if=/tmp/foo.bar of=/tmp/foo.bar1 bs=1m conv=sparse
10+0 records in
10+0 records out
$ ls -l /tmp/foo.bar /tmp/foo.bar1
-rw-r--r-- 1 sobomax wheel 10485760 Feb 9 23:59 /tmp/foo.bar
-rw-r--r-- 1 sobomax wheel 0 Feb 9 23:59 /tmp/foo.bar1
$ uname -a
FreeBSD abc.sippysoft.com 10.3-PRERELEASE FreeBSD 10.3-PRERELEASE #1
80de3e2(master)-dirty: Tue Feb 2 12:19:57 PST 2016
sobo...@abc.sippysoft.com:/usr/obj/usr/home/sobomax/projects/freebsd103/sys/VAN01
amd64
ktrace ends with:
3150 dd RET read 1048576/0x100000
3150 dd CALL read(0x3,0x801009000,0x100000)
3150 dd GIO fd 3 read 0 bytes
""
3150 dd RET read 0
3150 dd CALL lseek(0x4,0x900000,SEEK_CUR)
3150 dd RET lseek 9437184/0x900000
3150 dd CALL close(0x4)
3150 dd RET close 0
3150 dd CALL write(0x2,0x7fffffffe2c0,0x21)
3150 dd GIO fd 2 wrote 33 bytes
"10+0 records in
10+0 records out
"
3150 dd RET write 33/0x21
3150 dd CALL write(0x2,0x7fffffffe2c0,0x43)
3150 dd GIO fd 2 wrote 67 bytes
"10485760 bytes transferred in 0.008217 secs (1276090675 bytes/sec)
"
3150 dd RET write 67/0x43
3150 dd CALL sigprocmask(SIG_BLOCK,0x800822a38,0x7fffffffe780)
3150 dd RET sigprocmask 0
3150 dd CALL sigprocmask(SIG_SETMASK,0x800822a4c,0)
3150 dd RET sigprocmask 0
3150 dd CALL sigprocmask(SIG_BLOCK,0x800822a38,0x7fffffffe310)
3150 dd RET sigprocmask 0
3150 dd CALL sigprocmask(SIG_SETMASK,0x800822a4c,0)
3150 dd RET sigprocmask 0
3150 dd CALL sigprocmask(SIG_BLOCK,0x800822a38,0x7fffffffe310)
3150 dd RET sigprocmask 0
3150 dd CALL sigprocmask(SIG_SETMASK,0x800822a4c,0)
3150 dd RET sigprocmask 0
3150 dd CALL exit(0)
Looking at the code in question I don't see how could it have worked. Look at
the following piece of code in your diff for example:
+ if (force && cnt == 0) {
+ pending -= last_sp;
+ assert(outp == out.db);
+ memset(outp, 0, cnt);
+ }
When the branch is taken, cnt is 0, so at the very least memset(x, y, 0) is
NOP. Later on, write(2) is conditional on cnt != 0, so that it's never taken.
As a result, lseek is the last operation the file sees.
Also, for what it's worth, you can use ftruncate(2) instead of write() for
regular sparse files to ensure correct size. That would write just as much data
as needed to the end. I've made a quick and dirty patch, that seems to be
working better than current code at least:
http://sobomax.sippysoft.com/dd.diff
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