* [filesystem] struct of m_inode
@ 2013-03-02 2:28 lx
2013-03-02 2:46 ` Valdis.Kletnieks at vt.edu
0 siblings, 1 reply; 2+ messages in thread
From: lx @ 2013-03-02 2:28 UTC (permalink / raw)
To: kernelnewbies
Hi, I'm learning the kernel of 0.12, and the function in inode.c:
####################################################################
static int _bmap(struct m_inode * inode,int block,int create)
{
struct buffer_head * bh;
int i;
if (block<0)
panic("_bmap: block<0");
if (block >= 7+512+512*512)
panic("_bmap: block>big");
if (block<7) {
if (create && !inode->i_zone[block])
if (inode->i_zone[block]=new_block(inode->i_dev)) {
inode->i_ctime=CURRENT_TIME;
inode->i_dirt=1;
}
return inode->i_zone[block];
}
block -= 7;
if (block<512) {
if (create && !inode->i_zone[7])
if (inode->i_zone[7]=new_block(inode->i_dev)) {
inode->i_dirt=1;
inode->i_ctime=CURRENT_TIME;
}
if (!inode->i_zone[7])
return 0;
if (!(bh = bread(inode->i_dev,inode->i_zone[7])))
return 0;
i = ((unsigned short *) (bh->b_data))[block];
if (create && !i)
if (i=new_block(inode->i_dev)) {
((unsigned short *) (bh->b_data))[block]=i;
bh->b_dirt=1;
}
brelse(bh);
return i;
}
block -= 512;
if (create && !inode->i_zone[8])
if (inode->i_zone[8]=new_block(inode->i_dev)) {
inode->i_dirt=1;
inode->i_ctime=CURRENT_TIME;
}
if (!inode->i_zone[8])
return 0;
if (!(bh=bread(inode->i_dev,inode->i_zone[8])))
return 0;
i = ((unsigned short *)bh->b_data)[block>>9];
if (create && !i)
if (i=new_block(inode->i_dev)) {
((unsigned short *) (bh->b_data))[block>>9]=i;
bh->b_dirt=1;
}
brelse(bh);
if (!i)
return 0;
if (!(bh=bread(inode->i_dev,i)))
return 0;
i = ((unsigned short *)bh->b_data)[block&511];
if (create && !i)
if (i=new_block(inode->i_dev)) {
((unsigned short *) (bh->b_data))[block&511]=i;
bh->b_dirt=1;
}
brelse(bh);
return i;
}
########################################################################
"if (block >= 7+512+512*512)" because the i_zone[9].
But the question is why the i_zone[7] can repesent 512 , and i_zone[8] can
repesent 512*512 ?
Thank you.
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* [filesystem] struct of m_inode
2013-03-02 2:28 [filesystem] struct of m_inode lx
@ 2013-03-02 2:46 ` Valdis.Kletnieks at vt.edu
0 siblings, 0 replies; 2+ messages in thread
From: Valdis.Kletnieks at vt.edu @ 2013-03-02 2:46 UTC (permalink / raw)
To: kernelnewbies
On Sat, 02 Mar 2013 10:28:26 +0800, lx said:
> "if (block >= 7+512+512*512)" because the i_zone[9].
> But the question is why the i_zone[7] can repesent 512 , and i_zone[8] can
> repesent 512*512 ?
Sngle, double, and triple indirect blocks...
http://en.wikipedia.org/wiki/Inode_pointer_structure
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