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how to get device block number of a file

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0

I am using the code below to get the block number of a file:

int get_block (int fd, int logical_block)

 int ret;
 ret = ioctl (fd, FIBMAP, &logical_block);
 if (ret <0 )
 perror ("ioctl");
 return -1;
 
 return logical_block;

int get_nr_blocks (int fd)

 struct stat buf;
 int ret,blocks_in_4k;
 ret = fstat (fd, &buf);
 if ( ret < 0 ) 
 perror ("fstat");
 return -1;
 
 blocks_in_4k = buf.st_blocks/8;
 return blocks_in_4k;

void print_blocks (int fd)

 int nr_blocks,i;
 int f_phys_block,e_phys_block;
 nr_blocks = get_nr_blocks (fd);
 if (nr_blocks <0 ) 
 fprintf (stderr, "get_nr_blocks failed!n");
 return;
 
 if (nr_blocks == 0) 
 printf( "no allocated blocksn");
 return;
 else if ( nr_blocks == 1)
 printf ("1 blocknn");
 else
 printf ("this file has %d blocksnn",nr_blocks);

 for (i =0; i <nr_blocks; i++) 
 int phys_block;
 phys_block = get_block (fd, i );
 if (phys_block <0 ) 
 fprintf (stderr, "get_block failed!n");
 return;
 
 if ( !phys_block)
 continue;
 if ( i == 0 )
 f_phys_block=phys_block;
 if ( i == nr_blocks -1 )
 e_phys_block=phys_block;
 printf ("(%u, %u),",i,phys_block);
 
 if ( nr_blocks != e_phys_block - f_phys_block + 1) 
 printf ("nthis file is fragmented n");
 printf ("total blocks <%u>,first physical block <%u>, the last physical block <%u>n",nr_blocks,f_phys_block,e_phys_block);
 
 putchar ('n');

int main (int argc, char *argv[] )

 int fd;
 if (argc <2 ) 
 fprintf (stderr, "usage: %s <file>n",argv[0]);
 
 fd = open (argv[1],O_RDONLY);
 if (fd <0) 
 perror ("open");
 return 1;
 
 print_blocks(fd);
 return 0;

It gives me output like this:
this file has 32 blocks (4kb per block)
(0, 99596),(1, 99597),(2, 99598),(3, 99599)
But after I made the image of the device using command dd, which the file is actually stored in, the block number didn't indicate the real block offset of the file. What should I do to get the real device block offset?

linux ioctl

share|improve this question

asked Mar 24 at 2:45

S. EzrealS. Ezreal

1

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  after I made the image of the device using command dd, which the file is actually stored in how? You can create a function from your program and add system("dd ...") call to make an MCVE.
  
  – Kamil Cuk
  Mar 24 at 3:12
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I know the file is on the device "/dev/block/mmcblk0" and I want to get the offset of the file in the image. What is MCVE
  
  – S. Ezreal
  Mar 24 at 3:40
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  MCVE. "the file is on the device" - there is also filesystem layer in between. So you have a file, within a filesystem, within a partition on a block device (sdcard). You want to know on which byte within the block device the file starts, right? What filesystem are you using?
  
  – Kamil Cuk
  Mar 24 at 3:43
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I think the best and most reliable way is to write a long unique string to the file. Then open the /dev/block/mmcblk0 as a normal file and search for the string. A filesystem can compress the file, duplicate it's contents etc. etc.
  
  – Kamil Cuk
  Mar 24 at 3:50
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I am doing this on android so the filesystem is ext4. I tried this way but it's a relatively time-costy operation and it want to do it faster. Can you give me a clue?
  
  – S. Ezreal
  Mar 24 at 4:09
  
  

  
  
  
  

add a comment | 

0

I am using the code below to get the block number of a file:

int get_block (int fd, int logical_block)

 int ret;
 ret = ioctl (fd, FIBMAP, &logical_block);
 if (ret <0 )
 perror ("ioctl");
 return -1;
 
 return logical_block;

int get_nr_blocks (int fd)

 struct stat buf;
 int ret,blocks_in_4k;
 ret = fstat (fd, &buf);
 if ( ret < 0 ) 
 perror ("fstat");
 return -1;
 
 blocks_in_4k = buf.st_blocks/8;
 return blocks_in_4k;

void print_blocks (int fd)

 int nr_blocks,i;
 int f_phys_block,e_phys_block;
 nr_blocks = get_nr_blocks (fd);
 if (nr_blocks <0 ) 
 fprintf (stderr, "get_nr_blocks failed!n");
 return;
 
 if (nr_blocks == 0) 
 printf( "no allocated blocksn");
 return;
 else if ( nr_blocks == 1)
 printf ("1 blocknn");
 else
 printf ("this file has %d blocksnn",nr_blocks);

 for (i =0; i <nr_blocks; i++) 
 int phys_block;
 phys_block = get_block (fd, i );
 if (phys_block <0 ) 
 fprintf (stderr, "get_block failed!n");
 return;
 
 if ( !phys_block)
 continue;
 if ( i == 0 )
 f_phys_block=phys_block;
 if ( i == nr_blocks -1 )
 e_phys_block=phys_block;
 printf ("(%u, %u),",i,phys_block);
 
 if ( nr_blocks != e_phys_block - f_phys_block + 1) 
 printf ("nthis file is fragmented n");
 printf ("total blocks <%u>,first physical block <%u>, the last physical block <%u>n",nr_blocks,f_phys_block,e_phys_block);
 
 putchar ('n');

int main (int argc, char *argv[] )

 int fd;
 if (argc <2 ) 
 fprintf (stderr, "usage: %s <file>n",argv[0]);
 
 fd = open (argv[1],O_RDONLY);
 if (fd <0) 
 perror ("open");
 return 1;
 
 print_blocks(fd);
 return 0;

It gives me output like this:
this file has 32 blocks (4kb per block)
(0, 99596),(1, 99597),(2, 99598),(3, 99599)
But after I made the image of the device using command dd, which the file is actually stored in, the block number didn't indicate the real block offset of the file. What should I do to get the real device block offset?

linux ioctl

share|improve this question

asked Mar 24 at 2:45

S. EzrealS. Ezreal

1

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  after I made the image of the device using command dd, which the file is actually stored in how? You can create a function from your program and add system("dd ...") call to make an MCVE.
  
  – Kamil Cuk
  Mar 24 at 3:12
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I know the file is on the device "/dev/block/mmcblk0" and I want to get the offset of the file in the image. What is MCVE
  
  – S. Ezreal
  Mar 24 at 3:40
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  MCVE. "the file is on the device" - there is also filesystem layer in between. So you have a file, within a filesystem, within a partition on a block device (sdcard). You want to know on which byte within the block device the file starts, right? What filesystem are you using?
  
  – Kamil Cuk
  Mar 24 at 3:43
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I think the best and most reliable way is to write a long unique string to the file. Then open the /dev/block/mmcblk0 as a normal file and search for the string. A filesystem can compress the file, duplicate it's contents etc. etc.
  
  – Kamil Cuk
  Mar 24 at 3:50
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I am doing this on android so the filesystem is ext4. I tried this way but it's a relatively time-costy operation and it want to do it faster. Can you give me a clue?
  
  – S. Ezreal
  Mar 24 at 4:09
  
  

  
  
  
  

add a comment | 

I am using the code below to get the block number of a file:

int get_block (int fd, int logical_block)

 int ret;
 ret = ioctl (fd, FIBMAP, &logical_block);
 if (ret <0 )
 perror ("ioctl");
 return -1;
 
 return logical_block;

int get_nr_blocks (int fd)

 struct stat buf;
 int ret,blocks_in_4k;
 ret = fstat (fd, &buf);
 if ( ret < 0 ) 
 perror ("fstat");
 return -1;
 
 blocks_in_4k = buf.st_blocks/8;
 return blocks_in_4k;

void print_blocks (int fd)

 int nr_blocks,i;
 int f_phys_block,e_phys_block;
 nr_blocks = get_nr_blocks (fd);
 if (nr_blocks <0 ) 
 fprintf (stderr, "get_nr_blocks failed!n");
 return;
 
 if (nr_blocks == 0) 
 printf( "no allocated blocksn");
 return;
 else if ( nr_blocks == 1)
 printf ("1 blocknn");
 else
 printf ("this file has %d blocksnn",nr_blocks);

 for (i =0; i <nr_blocks; i++) 
 int phys_block;
 phys_block = get_block (fd, i );
 if (phys_block <0 ) 
 fprintf (stderr, "get_block failed!n");
 return;
 
 if ( !phys_block)
 continue;
 if ( i == 0 )
 f_phys_block=phys_block;
 if ( i == nr_blocks -1 )
 e_phys_block=phys_block;
 printf ("(%u, %u),",i,phys_block);
 
 if ( nr_blocks != e_phys_block - f_phys_block + 1) 
 printf ("nthis file is fragmented n");
 printf ("total blocks <%u>,first physical block <%u>, the last physical block <%u>n",nr_blocks,f_phys_block,e_phys_block);
 
 putchar ('n');

int main (int argc, char *argv[] )

 int fd;
 if (argc <2 ) 
 fprintf (stderr, "usage: %s <file>n",argv[0]);
 
 fd = open (argv[1],O_RDONLY);
 if (fd <0) 
 perror ("open");
 return 1;
 
 print_blocks(fd);
 return 0;

It gives me output like this:
this file has 32 blocks (4kb per block)
(0, 99596),(1, 99597),(2, 99598),(3, 99599)
But after I made the image of the device using command dd, which the file is actually stored in, the block number didn't indicate the real block offset of the file. What should I do to get the real device block offset?

linux ioctl

share|improve this question

asked Mar 24 at 2:45

S. EzrealS. Ezreal

1

int get_block (int fd, int logical_block)

 int ret;
 ret = ioctl (fd, FIBMAP, &logical_block);
 if (ret <0 )
 perror ("ioctl");
 return -1;
 
 return logical_block;

int get_nr_blocks (int fd)

 struct stat buf;
 int ret,blocks_in_4k;
 ret = fstat (fd, &buf);
 if ( ret < 0 ) 
 perror ("fstat");
 return -1;
 
 blocks_in_4k = buf.st_blocks/8;
 return blocks_in_4k;

void print_blocks (int fd)

 int nr_blocks,i;
 int f_phys_block,e_phys_block;
 nr_blocks = get_nr_blocks (fd);
 if (nr_blocks <0 ) 
 fprintf (stderr, "get_nr_blocks failed!n");
 return;
 
 if (nr_blocks == 0) 
 printf( "no allocated blocksn");
 return;
 else if ( nr_blocks == 1)
 printf ("1 blocknn");
 else
 printf ("this file has %d blocksnn",nr_blocks);

 for (i =0; i <nr_blocks; i++) 
 int phys_block;
 phys_block = get_block (fd, i );
 if (phys_block <0 ) 
 fprintf (stderr, "get_block failed!n");
 return;
 
 if ( !phys_block)
 continue;
 if ( i == 0 )
 f_phys_block=phys_block;
 if ( i == nr_blocks -1 )
 e_phys_block=phys_block;
 printf ("(%u, %u),",i,phys_block);
 
 if ( nr_blocks != e_phys_block - f_phys_block + 1) 
 printf ("nthis file is fragmented n");
 printf ("total blocks <%u>,first physical block <%u>, the last physical block <%u>n",nr_blocks,f_phys_block,e_phys_block);
 
 putchar ('n');

int main (int argc, char *argv[] )

 int fd;
 if (argc <2 ) 
 fprintf (stderr, "usage: %s <file>n",argv[0]);
 
 fd = open (argv[1],O_RDONLY);
 if (fd <0) 
 perror ("open");
 return 1;
 
 print_blocks(fd);
 return 0;

share|improve this question

asked Mar 24 at 2:45

S. EzrealS. Ezreal

1

share|improve this question

asked Mar 24 at 2:45

S. EzrealS. Ezreal

1

asked Mar 24 at 2:45

S. EzrealS. Ezreal

1

asked Mar 24 at 2:45

S. EzrealS. Ezreal

1