Hi guys,
I was experimenting with loopback and crypto
(to check performance when run over a file on an
inferior nonindexed fat32 filesystem)
and run into the following problem:
when reading over the end of the device vmstat started
to show tremendous 'bi' activity:
- 0 0 0 40552 70956 23284 78876 4 0 4 0 107 246
0 0 100
0 0 0 40552 70956 23284 78876 0 0 0 0 101 176
0 0 100
0 0 0 40552 70956 23284 78876 0 0 0 0 101 229
0 0 100
1 0 0 40552 62280 23284 87468 0 0 8596 0 174 313 2
27 71
1 0 0 40552 36936 23284 112812 0 0 25344 0 300 466 0
70 30
procs memory swap io
system cpu
r b w swpd free buff cache si so bi bo in cs us
sy id
3 0 0 40552 8056 23284 138412 0 0 25600 0 302 426 3
68 29
1 0 0 40676 4360 20224 145764 0 1628 18176 1628 315 518
1 48 51
1 0 1 40676 4424 20224 145764 0 0 25600 128 325 720 0
86 14
0 1 1 40676 4456 20224 145892 0 0 24832 0 293 712 0
67 33
1 1 1 40676 4192 19636 147596 0 208 17664 208 267 536 3
44 53
2 0 1 40676 4000 17168 150016 0 0 20480 4 265 621 1
57 42
# dd if=/dev/loop1 of=/tmp/del count=2 skip=709700 bs=1024
2+0 records in
2+0 records out (just OK)
# dd if=/dev/loop1 of=/tmp/del count=2 skip=729700 bs=1024
... because of readover dd never returned!!
When killing dd the abnormal 'bi' activity goes away.
--------------
I straced dd:
...
close(0) = 0
open("/dev/loop2", O_RDONLY|0x8000) = 0
close(1) = 0
open("/tmp/del", O_WRONLY|O_CREAT|O_TRUNC|0x8000, 0666) = 1
...
fstat64(0, 0xbffffaec) = 0
_llseek(0, 736972800, 0xbffffb44, SEEK_CUR) = -1 EINVAL (Invalid
argument)
read(0, "Q\247Q\342+\220T\251\2553\363\300\t\345\23\f\230\345\336"...,
1024) = 1024
read(0, "@\210t\340$\277\224\234\25\377\25\325\20*D\302\270yRc\n"...,
1024) = 1024
read(0, "&\354\363@\307\346s\21\305\267\262\242\302\252\322\215"...,
1024) = 1024
.......infinite loop....
------------------- System:
Debian 2.3:
ii fileutils 4.1-7 GNU file management utilities.
ii libc6 2.2.4-5 GNU C Library: Shared libraries and
Timezone
------------------
Using Linux 2.4.17 kernel with loop-jari-2.4.16.0.patch and
patch-int-2.4.17.0.bz2
international patch.
/dev/loop2: [0307]:1256 (idea-cbc) offset 0, undefined encryption
It seems to be independent of the cipher used.
Should something return some error instead of failing silently?
BTW mke2fs seems to find out the size of the device just OK.
Does dd ignore the return value of _llseek()?
Note: I did not experience any instability relating to this.
On the other hand this is perfect for comparing cipher
performance ;-))
what else should I check?
thanx, guys; GNU's great, keep up the good work:
Marcell
--
You'll never see all the places, or read all the books, but fortunately,
they're not all recommended.
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