Hi friends,
I am trying to learn filesystems and writing a small module. Till now
I am able to do simple mount,cd commands. However in order to support
creating new files, I have implemented the below function. However I
am stuck at few points. It would be of great help if someone can
clarify.
1) When is d_instantiate needed. Is it required always ?? . As far as
i understand it attaches the inode to the dentry object and may not be
needed always.
2) Once I have got the new inode * by a call to new_inode, how do I
fill my file system specific data.. ie... i_private member is
initialised as NULL.
Should I allocate memory for my inode and set i_private to it ??........
int nngfs_create(struct inode *dir, struct dentry *dentry, int
mode,struct nameidata *nd){
int inum=0,ret=0;
struct buffer_head *bh;
struct inode *newnip;
struct nngfs_inode *nino;
struct super_block *sb = dir->i_sb;
struct nngfs_info *nsb = (struct nngfs_info *)(sb->s_fs_info);
struct nngfs_superblock *n_sb = nsb->ngfs_sb;
//See if the entry already exists in the dir
ret = nngfs_find_entry(dir,dentry->d_name.name);
if(ret!=-1){
return ERR_PTR(-EEXIST);
}
//See the bitmap and get the inode number
inum = Get_free_inode_number(n_sb);
if(inum == -1){
printk(KERN_INFO "NGFS (%s) :Got free inode number =
%d\n",__FUNCTION__,inum);
return ERR_PTR(-ENOSPC);
}
//Allocate the new inode
newnip = new_inode(sb);
if(!newnip){
printk(KERN_INFO "NGFS (%s) :Could not allocate free
inode\n",__FUNCTION__);
return ERR_PTR(-ENOSPC);
} newnip->i_ino = inum;
//Add the name information to dir entry
if(nngfs_dir_add(dir,inum,dentry->d_name.name)){
printk(KERN_INFO "NGFS (%s) :Could not allocate free
inode\n",__FUNCTION__);
return ERR_PTR(-EMFILE);
}
bh = (struct buffer_head *)(nsb->sbh);
n_sb->inode_bitmap=setbit(n_sb->inode_bitmap,inum);
newnip->i_ino = inum;
dir->i_nlink++;
newnip->i_mode = NNGFS_FILE;
newnip->i_atime = newnip->i_mtime = newnip->i_ctime = CURRENT_TIME;
newnip->i_uid = dir->i_uid;
newnip->i_gid = dir->i_gid;
/* Stuck below this point. Not sure what to do */
d_instantiate(dir,newnip);
nino = (struct nngfs_inode *)newnip->i_private;
#ifdef DEBUG
printk(KERN_CRIT "NGFS (%s)(%d) : Going to reference .... [%p]
",__FUNCTION__,__LINE__,nino);
#endif
nino->filetype = NNGFS_FILE;
#ifdef DEBUG
printk(KERN_CRIT "NGFS (%s)(%d) : Seems referencing is ok ....
",__FUNCTION__,__LINE__);
#endif
nino->atime = nino->mtime = nino->ctime = CURRENT_TIME;
nino->uid = dir->i_uid;
nino->gid = dir->i_gid;
sb->s_dirt=1;
mark_buffer_dirty(bh); //Write the new bitmap to disk
mark_inode_dirty(newnip);
mark_inode_dirty(dir);
return 0;
}
Note that i am writing this only for learning, so not much concerned
about other details like atomicity and race conditions etc. at this
point. Also I am not using any caches for my inode allocation.
Appreciate any help/suggestions.
--
Thanks & Regards,
********************************************
Manish Katiyar ( http://mkatiyar.googlepages.com )
3rd Floor, Fair Winds Block
EGL Software Park
Off Intermediate Ring Road
Bangalore 560071, India
***********************************************
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