On 2010-08-10, at 10:23, Toshiyuki Okajima wrote:
> Table. the max file size which we can write or seek
> at each filesystem feature tuning and file flag setting
> +===============================+===============================+
> | | |
> | !EXT4_EXTENTS_FL | EXT4_EXTETNS_FL |
> | | |
> +-------------------------------+-------------------------------+
> | write: 2194719883264 | write: -------------- |
> | seek: 2199023251456 | seek: -------------- |
> +-------------------------------+-------------------------------+
> | write: 4402345721856 | write: 17592186044415 |
> | seek: 17592186044415 | seek: 17592186044415 |
> +-------------------------------+-------------------------------+
Interesting. The 2TB vs. 4TB difference for block-mapped files is due to the removal of the 2^32 sectors limit imposed by i_blocks, and is not strictly related to extents.
> +loff_t ext4_llseek(struct file *file, loff_t offset, int origin)
> +{
> + struct inode *inode = file->f_mapping->host;
> + loff_t maxbytes;
> +
> + mutex_lock(&inode->i_mutex);
> + if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)))
> + maxbytes = EXT4_SB(inode->i_sb)->s_bitmap_maxbytes;
> + else
> + maxbytes = inode->i_sb->s_maxbytes;
This part doesn't really have to be under i_mutex. Otherwise, the patch looks reasonable.
> + switch (origin) {
> + case SEEK_END:
> + offset += inode->i_size;
> + break;
> + case SEEK_CUR:
> + if (offset == 0) {
> + mutex_unlock(&inode->i_mutex);
> + return file->f_pos;
> + }
> + offset += file->f_pos;
> + break;
> + }
> +
> + if (offset < 0 || offset > maxbytes) {
> + mutex_unlock(&inode->i_mutex);
> + return -EINVAL;
> + }
> +
> + if (offset != file->f_pos) {
> + file->f_pos = offset;
> + file->f_version = 0;
> + }
> + mutex_unlock(&inode->i_mutex);
> +
> + return offset;
> +}
It's too bad that we have to duplicate the whole generic_file_llseek() code here, but I don't think there is a better solution. However, it is worthwhile to add a comment to this function like:
/* copied from generic_file_llseek() to handle both block-mapped and
* extent-mapped maxbytes values. Should otherwise be identical. */
Cheers, Andreas
--
Andreas Dilger
Lustre Technical Lead
Oracle Corporation Canada Inc.
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