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Dear friends:
Thanks for your
answers.
This time, I include my test source code, strace output and
xfs_bmap ?v results here, wish it helps to solve the problem.
======================
My source code is as
followed:
======================
#include <stdlib.h>
…
#define BIG_FILE
"./bigone"
int main(int argc, char **argv)
{
FILE
*fd;
__off64_t myoff;
if( (fd=(FILE *)fopen64("./bigone", "rb")) == NULL
)
{
perror( "\nopen bigone fail\n"
);
exit(0);
}
myoff=(__off64_t)1000000*(__off64_t)2200;
printf("\n
begin to seek \n");
if( fseeko64(fd,myoff, SEEK_SET) !=0
)
{
perror("\nseek
fail\n");
exit(0);
}
else
{
printf("\nseek
ok!!\n");
}
fclose(fd);
return
1;
}
------ end of source code --------
==============================
Strace result is as
following:
==============================
execve("./a.out", ["./a.out"], [/* 20 vars */]) =
0
brk(0)
= 0x8049758
old_mmap(NULL, 4096, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x40014000
open("/etc/ld.so.preload",
O_RDONLY) = -1 ENOENT (No such file or
directory)
open("/etc/ld.so.cache", O_RDONLY) =
3
fstat(3, {st_mode=S_IFREG|0644, st_size=11671, ...}) = 0
old_mmap(NULL,
11671, PROT_READ, MAP_PRIVATE, 3, 0) =
0x40015000
close(3)
= 0
open("/lib/libc.so.6",
O_RDONLY) = 3
fstat(3,
{st_mode=S_IFREG|0755, st_size=4101324, ...}) = 0
read(3,
"\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\210\212"..., 4096) =
4096
old_mmap(NULL, 1001564, PROT_READ|PROT_EXEC, MAP_PRIVATE, 3, 0) =
0x40018000
mprotect(0x40105000, 30812, PROT_NONE) =
0
old_mmap(0x40105000, 16384, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED, 3,
0xec000) = 0x40105000
old_mmap(0x40109000, 14428, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) =
0x40109000
close(3)
= 0
mprotect(0x40018000, 970752, PROT_READ|PROT_WRITE) =
0
mprotect(0x40018000, 970752, PROT_READ|PROT_EXEC) = 0
munmap(0x40015000,
11671)
=
0
personality(PER_LINUX)
=
0
getpid()
=
1138
brk(0)
=
0x8049758
brk(0x8049820)
=
0x8049820
brk(0x804a000)
= 0x804a000
open("./bigone", O_RDONLY|O_LARGEFILE) = 3
fstat64(0x1,
0xbffff588)
= 0
old_mmap(NULL, 65536, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS,
-1, 0) = 0x4010d000
fstat64(0x3,
0xbffffb6c)
= 0
old_mmap(NULL, 65536, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS,
-1, 0) = 0x4011d000
_llseek(3, 18446744071614562304, [2199977984], SEEK_SET)
= 0
read(3, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"...,
22016) =
22016
close(3)
= 0
munmap(0x4011d000,
65536)
= 0
write(1, "\n begin to seek \n\nseek ok!!\n", 28
begin to seek
seek ok!!
) = 28
munmap(0x4010d000,
65536)
=
0
_exit(1)
= ?
------ end of strace result --------
=====================
Information about file
bigone
=====================
I generate “bigone” by using:
dd
if=/dev/zero of=bigone bs=1024k count=4500
[root]# xfs_bmap -v bigone
bigone:
EXT:
FILE-OFFSET
BLOCK-RANGE AG
AG-OFFSET
TOTAL
0: [0..1959935]:
96..1960031 0
(96..1960031) 1959936
1: [1959936..3917823]:
1974904..3932791 1 (64..1957951) 1957888
2: [3917824..5853183]: 3949744..5885103 2 (64..1935423)
1935360
3: [5853184..7811071]: 5924584..7882471 3
(64..1957951) 1957888
4: [7811072..9215999]:
7909024..9313951 4 (9664..1414591) 1404928
Thank you very much.
yangxy
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