* pread() from /dev/sda fails with: Illegal seek
@ 2020-01-11 14:10 David Balažic
2020-01-11 20:24 ` Enrique Perez-Terron
2020-01-12 16:59 ` Christian Franke
0 siblings, 2 replies; 3+ messages in thread
From: David Balažic @ 2020-01-11 14:10 UTC (permalink / raw)
To: cygwin
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Hi!
I'm porting an app from Linux to Cygwin and stumbled on this problem:
pread on /dev/sda fails with Illegal seek.
The simplified code is:
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
int main(int argc, char *argv[])
{
unsigned int sector_size = 512;
void *buf = calloc(sector_size,1);
int fd = open("/dev/sda", O_DIRECT | O_RDONLY);
if (-1 == pread(fd, buf, sector_size, 0)) {
perror("pread failed");
}
}
# g++ test.cc
# ./a # run as adnministrator
pread failed: Illegal seek
Why is that?
cygcheck -s output attached.
Summary: cygwin 3.1.2-1 , Windows 8.1 , all 64 bit
Regards,
David
[-- Attachment #2: cygcheck-s --]
[-- Type: application/octet-stream, Size: 12161 bytes --]
Cygwin Configuration Diagnostics
Current System Time: Sat Jan 11 14:07:55 2020
Windows 8.1 Professional Ver 6.3 Build 9600
Path: C:\cygwin64\usr\local\bin
C:\cygwin64\bin
C:\Windows\system32
C:\Windows
C:\Windows\System32\Wbem
C:\Windows\System32\WindowsPowerShell\v1.0
C:\Program Files (x86)\NVIDIA Corporation\PhysX\Common
Output from C:\cygwin64\bin\id.exe
UID: 197609(stein) GID: 197121(None)
197121(None) 197610(HomeUsers)
545(Users) 4(INTERACTIVE)
66049(CONSOLE LOGON) 11(Authenticated Users)
15(This Organization) 113(Local account)
4095(CurrentSession) 66048(LOCAL)
262154(NTLM Authentication) 401408(Medium Mandatory Level)
SysDir: C:\Windows\system32
WinDir: C:\Windows
USER = 'stein'
PWD = '/home/stein/hdubench'
HOME = '/home/stein'
Use '-r' to scan registry
obcaseinsensitive set to 1
Cygwin installations found in the registry:
System: Key: e022582115c10879 Path: C:\cygwin64
System: Key: 9a234e4d83618c4a Path: C:\Users\stein\Documents\x\x\x64_win (ORPHANED)
User: Key: e022582115c10879 Path: C:\cygwin64
User: Key: 6435883e1e7fe6b2 Path: C:\Program Files (x86)\Exact Audio Copy (ORPHANED)
User: Key: d67f57a3330a6cd6 Path: C:\Users\stein\Documents\x\x\john-1.9.0-jumbo-1-win64 (ORPHANED)
User: Key: 9a234e4d83618c4a Path: C:\Users\stein\Documents\x\x\x64_win (ORPHANED)
c: hd NTFS 323339Mb 66% CP CS UN PA FC QU
d: hd NTFS 953865Mb 80% CP CS UN PA FC QU Data1
e: hd NTFS 629999Mb 100% CP CS UN PA FC QU za backup fill
h: cd N/A N/A
i: fd N/A N/A
j: fd N/A N/A
k: fd N/A N/A
C:\cygwin64 / system binary,auto
C:\cygwin64\bin /usr/bin system binary,auto
C:\cygwin64\lib /usr/lib system binary,auto
cygdrive prefix /cygdrive user binary,posix=0,auto
Found: C:\cygwin64\bin\awk
-> C:\cygwin64\bin\gawk.exe
Found: C:\cygwin64\bin\bash.exe
Found: C:\cygwin64\bin\cat.exe
Found: C:\Windows\system32\certutil.exe
Not Found: clinfo
Found: C:\Windows\system32\comp.exe
Found: C:\Windows\system32\convert.exe
Found: C:\cygwin64\bin\cp.exe
Found: C:\cygwin64\bin\cpp.exe
Not Found: crontab
Not Found: curl
Found: C:\cygwin64\bin\expand.exe
Found: C:\Windows\system32\expand.exe
Found: C:\cygwin64\bin\find.exe
Found: C:\Windows\system32\find.exe
Found: C:\Windows\system32\ftp.exe
Found: C:\cygwin64\bin\gcc.exe
Not Found: gdb
Found: C:\cygwin64\bin\grep.exe
Found: C:\cygwin64\bin\hostname.exe
Found: C:\Windows\system32\hostname.exe
Found: C:\cygwin64\bin\kill.exe
Found: C:\Windows\system32\klist.exe
Found: C:\cygwin64\bin\ld.exe
Found: C:\cygwin64\bin\ls.exe
Found: C:\cygwin64\bin\make.exe
Found: C:\cygwin64\bin\mv.exe
Found: C:\Windows\system32\nslookup.exe
Not Found: patch
Not Found: perl
Found: C:\Windows\system32\replace.exe
Found: C:\cygwin64\bin\rm.exe
Found: C:\cygwin64\bin\sed.exe
Found: C:\cygwin64\bin\sh.exe
Found: C:\Windows\system32\shutdown.exe
Found: C:\cygwin64\bin\sort.exe
Found: C:\Windows\system32\sort.exe
Not Found: ssh
Found: C:\cygwin64\bin\tar.exe
Found: C:\cygwin64\bin\test.exe
Found: C:\cygwin64\bin\timeout.exe
Found: C:\Windows\system32\timeout.exe
Found: C:\cygwin64\bin\vi.exe
Not Found: vim
Found: C:\cygwin64\bin\whoami.exe
Found: C:\Windows\system32\whoami.exe
39k 2016/09/19 C:\cygwin64\bin\cygargp-0.dll
29k 2018/12/09 C:\cygwin64\bin\cygatomic-1.dll
19k 2018/12/20 C:\cygwin64\bin\cygattr-1.dll
246k 2019/03/05 C:\cygwin64\bin\cygblkid-1.dll
66k 2019/07/21 C:\cygwin64\bin\cygbz2-1.dll
39k 2017/09/03 C:\cygwin64\bin\cygcrypt-0.dll
2363k 2019/09/11 C:\cygwin64\bin\cygcrypto-1.0.0.dll
2416k 2019/09/13 C:\cygwin64\bin\cygcrypto-1.1.dll
347k 2019/03/05 C:\cygwin64\bin\cygfdisk-1.dll
27k 2015/11/17 C:\cygwin64\bin\cygffi-6.dll
56k 2019/07/28 C:\cygwin64\bin\cygformw-10.dll
137k 2019/03/29 C:\cygwin64\bin\cyggc-1.dll
119k 2018/01/16 C:\cygwin64\bin\cyggc-2.dll
70k 2018/12/09 C:\cygwin64\bin\cyggcc_s-seh-1.dll
46k 2019/07/10 C:\cygwin64\bin\cyggdbm-4.dll
527k 2017/01/21 C:\cygwin64\bin\cyggmp-10.dll
1472k 2019/07/29 C:\cygwin64\bin\cyggnutls-30.dll
148k 2018/12/09 C:\cygwin64\bin\cyggomp-1.dll
732k 2017/04/01 C:\cygwin64\bin\cygguile-17.dll
1333k 2018/08/07 C:\cygwin64\bin\cygguile-2.0-22.dll
33k 2017/02/13 C:\cygwin64\bin\cyghistory7.dll
168k 2019/02/19 C:\cygwin64\bin\cyghogweed-4.dll
1009k 2015/02/20 C:\cygwin64\bin\cygiconv-2.dll
114k 2019/07/29 C:\cygwin64\bin\cygidn2-0.dll
42k 2016/10/23 C:\cygwin64\bin\cygintl-8.dll
1039k 2015/09/20 C:\cygwin64\bin\cygisl-13.dll
1304k 2017/11/04 C:\cygwin64\bin\cygisl-15.dll
35k 2019/07/28 C:\cygwin64\bin\cygltdl-7.dll
144k 2019/07/21 C:\cygwin64\bin\cyglzma-5.dll
129k 2017/10/05 C:\cygwin64\bin\cyglzo2-2.dll
125k 2018/03/18 C:\cygwin64\bin\cygmagic-1.dll
168k 2018/01/23 C:\cygwin64\bin\cygman-2-7-6-1.dll
22k 2018/01/23 C:\cygwin64\bin\cygmandb-2-7-6-1.dll
28k 2019/07/28 C:\cygwin64\bin\cygmenuw-10.dll
92k 2018/03/17 C:\cygwin64\bin\cygmpc-3.dll
346k 2017/11/04 C:\cygwin64\bin\cygmpfr-4.dll
432k 2019/02/02 C:\cygwin64\bin\cygmpfr-6.dll
301k 2019/07/28 C:\cygwin64\bin\cygncursesw-10.dll
205k 2019/02/19 C:\cygwin64\bin\cygnettle-6.dll
1013k 2019/02/20 C:\cygwin64\bin\cygp11-kit-0.dll
14k 2019/07/28 C:\cygwin64\bin\cygpanelw-10.dll
467k 2019/04/05 C:\cygwin64\bin\cygpcre-1.dll
41k 2019/09/12 C:\cygwin64\bin\cygpipeline-1.dll
41k 2016/07/13 C:\cygwin64\bin\cygpopt-0.dll
65k 2019/07/21 C:\cygwin64\bin\cygpsl-5.dll
315k 2018/12/09 C:\cygwin64\bin\cygquadmath-0.dll
219k 2017/02/13 C:\cygwin64\bin\cygreadline7.dll
11k 2015/07/17 C:\cygwin64\bin\cygsigsegv-2.dll
150k 2019/03/05 C:\cygwin64\bin\cygsmartcols-1.dll
408k 2019/09/11 C:\cygwin64\bin\cygssl-1.0.0.dll
495k 2019/09/13 C:\cygwin64\bin\cygssl-1.1.dll
12k 2017/11/13 C:\cygwin64\bin\cygssp-0.dll
1400k 2018/12/09 C:\cygwin64\bin\cygstdc++-6.dll
68k 2019/07/29 C:\cygwin64\bin\cygtasn1-6.dll
57k 2019/07/28 C:\cygwin64\bin\cygticw-10.dll
1612k 2018/08/16 C:\cygwin64\bin\cygunistring-2.dll
27k 2019/03/05 C:\cygwin64\bin\cyguuid-1.dll
8k 2016/06/13 C:\cygwin64\bin\cygvtv-0.dll
8k 2016/06/13 C:\cygwin64\bin\cygvtv_stubs-0.dll
83k 2017/03/03 C:\cygwin64\bin\cygz.dll
3508k 2019/12/21 C:\cygwin64\bin\cygwin1.dll
Cygwin DLL version info:
DLL version: 3.1.2
DLL epoch: 19
DLL old termios: 5
DLL malloc env: 28
Cygwin conv: 181
API major: 0
API minor: 340
Shared data: 5
DLL identifier: cygwin1
Mount registry: 3
Cygwin registry name: Cygwin
Installations name: Installations
Cygdrive default prefix:
Build date:
Shared id: cygwin1S5
Can't find the cygrunsrv utility, skipping services check.
Cygwin Package Information
Package Version Status
_autorebase 001007-1 OK
alternatives 1.3.30c-10 OK
base-cygwin 3.8-1 OK
base-files 4.3-2 OK
bash 4.4.12-3 OK
binutils 2.29-1 OK
bzip2 1.0.8-1 OK
ca-certificates 2.32-1 OK
coreutils 8.26-2 OK
crypto-policies 20190218-1 OK
cygutils 1.4.16-2 OK
cygwin 3.1.2-1 OK
cygwin-devel 3.1.2-1 OK
dash 0.5.9.1-1 OK
diffutils 3.5-2 OK
editrights 1.03-1 OK
file 5.32-1 OK
findutils 4.6.0-1 OK
gawk 5.0.1-1 OK
gcc-core 7.4.0-1 OK
gcc-g++ 7.4.0-1 OK
getent 2.18.90-4 OK
grep 3.0-2 OK
groff 1.22.4-1 OK
gzip 1.8-1 OK
hostname 3.13-1 OK
info 6.7-1 OK
ipc-utils 1.0-2 OK
less 551-1 OK
libargp 20110921-3 OK
libatomic1 7.4.0-1 OK
libattr1 2.4.48-2 OK
libblkid1 2.33.1-1 OK
libbz2_1 1.0.8-1 OK
libcrypt0 2.1-1 OK
libfdisk1 2.33.1-1 OK
libffi6 3.2.1-2 OK
libgc1 8.0.4-1 OK
libgc2 7.6.2-3 OK
libgcc1 7.4.0-1 OK
libgdbm4 1.13-1 OK
libgmp10 6.1.2-1 OK
libgnutls30 3.6.9-1 OK
libgomp1 7.4.0-1 OK
libguile17 1.8.8-3 OK
libguile2.0_22 2.0.14-3 OK
libhogweed4 3.4.1-1 OK
libiconv 1.14-3 OK
libiconv2 1.14-3 OK
libidn2_0 2.2.0-1 OK
libintl8 0.19.8.1-2 OK
libisl13 0.14.1-1 OK
libisl15 0.16.1-1 OK
libltdl7 2.4.6-7 OK
liblzma5 5.2.4-1 OK
liblzo2_2 2.10-1 OK
libmpc3 1.1.0-1 OK
libmpfr4 3.1.6-1p1 OK
libmpfr6 4.0.2-1 OK
libncursesw10 6.1-1.20190727 OK
libnettle6 3.4.1-1 OK
libp11-kit0 0.23.15-1 OK
libpcre1 8.43-1 OK
libpipeline1 1.5.1-1 OK
libpopt-common 1.16-2 OK
libpopt0 1.16-2 OK
libpsl5 0.21.0-1 OK
libquadmath0 7.4.0-1 OK
libreadline7 7.0.3-3 OK
libsigsegv2 2.10-2 OK
libsmartcols1 2.33.1-1 OK
libssl1.0 1.0.2t-1 OK
libssl1.1 1.1.1d-1 OK
libssp0 6.4.0-4 OK
libstdc++6 7.4.0-1 OK
libtasn1_6 4.14-1 OK
libunistring2 0.9.10-1 OK
libuuid1 2.33.1-1 OK
libvtv0 5.4.0-1 OK
login 1.13-1 OK
lrzip 0.631-1 OK
lz4 1.7.5-1 OK
make 4.2.1-2 OK
man-db 2.7.6.1-1 OK
mintty 3.1.0-1 OK
ncurses 6.1-1.20190727 OK
openssl 1.1.1d-1 OK
p11-kit 0.23.15-1 OK
p11-kit-trust 0.23.15-1 OK
publicsuffix-list-dafsa 20190717-1 OK
pv 1.4.12-1 OK
rebase 4.4.4-1 OK
run 1.3.4-2 OK
sed 4.4-1 OK
tar 1.29-1 OK
terminfo 6.1-1.20190727 OK
terminfo-extra 6.1-1.20190727 OK
tzcode 2019c-1 OK
tzdata 2019c-1 OK
util-linux 2.33.1-1 OK
vim-minimal 8.1.1772-1 OK
w32api-headers 7.0.0-1 OK
w32api-runtime 7.0.0-1 OK
wget 1.19.1-2 OK
which 2.20-2 OK
windows-default-manifest 6.4-1 OK
xz 5.2.4-1 OK
zlib0 1.2.11-1 OK
Use -h to see help about each section
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^ permalink raw reply [flat|nested] 3+ messages in thread* Re: pread() from /dev/sda fails with: Illegal seek
2020-01-11 14:10 pread() from /dev/sda fails with: Illegal seek David Balažic
@ 2020-01-11 20:24 ` Enrique Perez-Terron
2020-01-12 16:59 ` Christian Franke
1 sibling, 0 replies; 3+ messages in thread
From: Enrique Perez-Terron @ 2020-01-11 20:24 UTC (permalink / raw)
To: cygwin
[-- Attachment #1: Type: text/plain, Size: 1118 bytes --]
Den 2020-01-11 15:10, skrev David Balažic:
> pread on /dev/sda fails with Illegal seek.
Confirmed on windows 10, 64-bit.
My code:
$ cat t.c
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <fcntl.h>
int main(int argc, char *argv[])
{
int fd = open("/dev/sda", O_RDONLY, 0);
if (fd < 0) {
fprintf(stderr, "%s. open /dev/sda: %m\n", argv[0]);
exit(1);
}
char *buffer = malloc(512);
if (!buffer) {
fprintf(stderr, "%s: Out of memory\n", argv[0]);
exit(1);
}
int result = pread(fd, buffer, 512, 0);
if (result < 0) {
fprintf(stderr, "%s: pread: %m\n", argv[0]);
exit(1);
}
printf("All right!\n");
return 0;
}
Running in a mintty as Administrator:
$ ./t
./t: pread: Illegal seek
$ uname -a
CYGWIN_NT-10.0 panter 3.1.2(0.340/5/3) 2019-12-21 15:25 x86_64 Cygwin
$ cc --version
cc (GCC) 7.4.0
Copyright (C) 2017 Free Software Foundation, Inc.
Regards,
Enrique Perez-Terron
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^ permalink raw reply [flat|nested] 3+ messages in thread* Re: pread() from /dev/sda fails with: Illegal seek
2020-01-11 14:10 pread() from /dev/sda fails with: Illegal seek David Balažic
2020-01-11 20:24 ` Enrique Perez-Terron
@ 2020-01-12 16:59 ` Christian Franke
1 sibling, 0 replies; 3+ messages in thread
From: Christian Franke @ 2020-01-12 16:59 UTC (permalink / raw)
To: cygwin
David Balažic wrote:
> I'm porting an app from Linux to Cygwin and stumbled on this problem:
>
> pread on /dev/sda fails with Illegal seek.
>
> The simplified code is:
>
> #include <fcntl.h>
> #include <stdio.h>
> #include <unistd.h>
> #include <stdlib.h>
>
> int main(int argc, char *argv[])
> {
> unsigned int sector_size = 512;
> void *buf = calloc(sector_size,1);
> int fd = open("/dev/sda", O_DIRECT | O_RDONLY);
> if (-1 == pread(fd, buf, sector_size, 0)) {
> perror("pread failed");
> }
> }
>
> # g++ test.cc
> # ./a # run as adnministrator
> pread failed: Illegal seek
>
> Why is that?
Cygwin implements pread() and pwrite() only for regular disk files. For
all other file types (including raw devices) these functions fail with
errno EPIPE ("Illegal seek").
According to POSIX, "pread() ... shall read from a given position in the
file without changing the file offset", see [1]. This must also hold if
the file descriptor is used in multiple threads or is duplicated or is
inherited from/to other processes. This cannot be easily emulated with
Windows API. See [2] for a related long comment in source code.
If the app you want to port uses the fd only locally in a single thread,
then something like this function may work:
ssize_t emul_pread(int fd, void *buf, size_t n, off_t offset)
{
 off_t oldoffs = lseek(fd, 0, SEEK_CUR);
 if (oldoffs == (off_t)-1)
   return -1;
 if (lseek(fd, offset, SEEK_SET) == (off_t)-1)
   return -1;
 ssize_t nr = read(fd, buf, n);
 if (lseek(fd, oldoffs, SEEK_SET) == (off_t)-1)
   return -1;
 return nr;
}
Sorry, not tested :-)
Regards,
Christian
[1]
https://pubs.opengroup.org/onlinepubs/9699919799/functions/pread.html
[2]
https://cygwin.com/git/gitweb.cgi?p=newlib-cygwin.git;a=blob;f=winsup/cygwin/fhandler_disk_file.cc;h=32381a0b0dbff6b7983ec8c4cec2f67dc5821939#l1479
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^ permalink raw reply [flat|nested] 3+ messages in thread
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2020-01-11 14:10 pread() from /dev/sda fails with: Illegal seek David Balažic
2020-01-11 20:24 ` Enrique Perez-Terron
2020-01-12 16:59 ` Christian Franke
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