On Tue, Jan 15, 2013 at 01:55:09PM -0500, Theodore Ts'o wrote:
> On Mon, Jan 14, 2013 at 10:18:30PM +0800, Zheng Liu wrote:
> > +static errcode_t ext2fs_file_llseek_data(ext2_file_t file, __u64 offset)
> > +{
> > + int ret_flags, flag = 1;
> > + ext2_filsys fs = file->fs;
> > + errcode_t retval;
> > +
> > + /*
> > + * If offset == EXT2_SEEK_OFFSET_INVALID, that means that
> > + * the caller wants to find the data from file->pos.
> > + */
> > + offset = offset != EXT2_SEEK_OFFSET_INVALID ? offset : file->pos;
> > + file->blockno = offset / fs->blocksize;
> > + while (file->blockno * fs->blocksize < EXT2_I_SIZE(&file->inode)) {
> > + retval = ext2fs_bmap2(fs, file->ino, &file->inode,
> > + BMAP_BUFFER, 0, file->blockno,
> > + &ret_flags, &file->physblock);
>
> Using bmap will certainly work, although as an optimization we can do
> much better for extents if we use the extents interface. I won't
> insist on this, though. (We can always optimize this later).
Yeah, it allows us to skip to the next data/hole directly if the extents
interface is used. But if we do that, we will need to handle
extent-based file and indirect-based file resptively like this.
if (inode->i_flags & EXT4_EXTENTS_FL) {
ext2fs_file_ext_llseek_data();
...
} else {
ext2fs_file_ind_llseek_data();
...
}
I am not sure whether it is too complicated or not for us. What do you
think?
Thanks,
- Zheng
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