Some Info

[Nifty Hat Mitch]

On Tue, Nov 09, 2004 at 12:07:14AM +0530, Kaustubh Ghosh wrote:
> 
> Can you(anyone) please tell me the answers to the following:

>   1.How many inodes are there in a single block ?

First we need to know what the block size is and more
on how the fs was built.

the man page for  mke2fs - create an ext2/ext3 filesystem
is rich on this topic.

Example mke2fs has these flage :

	-b block-size 

And this flag looks interesting but does not do what the name implies
to me.

	-i bytes-per-inode 

The dir /usr/include/ext2fs contains 90% of what you are looking for.
Look for type defs in the include files.  You can do the arithmetic by
hand or play with the header files and small 'c' programs that return
'sizeof' various structures.

Make sure that you understand the difference between a structure on
disk and the kernel data structures.
                                                     

You will see something like this....
/*
 * Structure of an inode on the disk
 */
struct ext2_inode {
        __u16   i_mode;         /* File mode */
        __u16   i_uid;          /* Low 16 bits of Owner Uid */
        __u32   i_size;         /* Size in bytes */
        __u32   i_atime;        /* Access time */
        __u32   i_ctime;        /* Creation time */
        __u32   i_mtime;        /* Modification time */
        __u32   i_dtime;        /* Deletion Time */
        __u16   i_gid;          /* Low 16 bits of Group Id */
        __u16   i_links_count;  /* Links count */
        __u32   i_blocks;       /* Blocks count */
        __u32   i_flags;        /* File flags */
        union {
                struct {
                        __u32  l_i_reserved1;
                } linux1;
                struct {
                        __u32  h_i_translator;
                } hurd1;
                struct {
                        __u32  m_i_reserved1;
                } masix1;
        } osd1;                         /* OS dependent 1 */
        __u32   i_block[EXT2_N_BLOCKS];/* Pointers to blocks */
        __u32   i_generation;   /* File version (for NFS) */
        __u32   i_file_acl;     /* File ACL */
        __u32   i_dir_acl;      /* Directory ACL */
        __u32   i_faddr;        /* Fragment address */
        union {
                struct {
                        __u8    l_i_frag;       /* Fragment number */
                        __u8    l_i_fsize;      /* Fragment size */

             
                        __u16   i_pad1;
                        __u16   l_i_uid_high;   /* these 2 fields    */
                        __u16   l_i_gid_high;   /* were reserved2[0] */
                        __u32   l_i_reserved2;
                } linux2;
                struct {
                        __u8    h_i_frag;       /* Fragment number */
                        __u8    h_i_fsize;      /* Fragment size */
                        __u16   h_i_mode_high;
                        __u16   h_i_uid_high;
                        __u16   h_i_gid_high;
                        __u32   h_i_author;
                } hurd2;
                struct {
                        __u8    m_i_frag;       /* Fragment number */
                        __u8    m_i_fsize;      /* Fragment size */
                        __u16   m_pad1;
                        __u32   m_i_reserved2[2];
                } masix2;
        } osd2;                         /* OS dependent 2 */
};
 

Does this help?




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