On Thu, May 13, 2021 at 02:09:26PM -0400, Theodore Ts'o wrote:

quoted

+
+	err = jbd2_journal_bmap(journal, log_offset, &block_start);
+	if (err) {
+		printk(KERN_ERR "JBD2: bad block at offset %lu", log_offset);
+		return err;
+	}

We could get rid of this, and instead make sure block_start is initialized
to ~((unsigned long long) 0).  Then in the loop we can do...

quoted

+
+	/*
+	 * use block_start - 1 to meet check for contiguous with previous region:
+	 * phys_block == block_stop + 1
+	 */
+	block_stop = block_start - 1;
+
+	for (block = log_offset; block < journal->j_total_len; block++) {
+		err = jbd2_journal_bmap(journal, block, &phys_block);
+		if (err) {
+			printk(KERN_ERR "JBD2: bad block at offset %lu", block);
+			return err;
+		}

		if (block_start == ~((unsigned long long) 0)) {
			block_start = phys_block;
			block_Stop = block_start - 1;
		}

quoted

+
+		if (block == journal->j_total_len - 1) {
+			block_stop = phys_block;
+		} else if (phys_block == block_stop + 1) {
+			block_stop++;
+			continue;
+		}
+
+		/*
+		 * not contiguous with prior physical block or this is last
+		 * block of journal, take care of the region
+		 */
+		byte_start = block_start * journal->j_blocksize;
+		byte_stop = block_stop * journal->j_blocksize;
+		byte_count = (block_stop - block_start + 1) *
+				journal->j_blocksize;
+
+		truncate_inode_pages_range(journal->j_dev->bd_inode->i_mapping,
+				byte_start, byte_stop);
+
+		if (flags & JBD2_ERASE_FLAG_DISCARD) {
+			err = blkdev_issue_discard(journal->j_dev,
+					byte_start >> SECTOR_SHIFT,
+					byte_count >> SECTOR_SHIFT,
+					GFP_NOFS, 0);
+		} else if (flags & JBD2_ERASE_FLAG_ZEROOUT) {
+			err = blkdev_issue_zeroout(journal->j_dev,
+					byte_start >> SECTOR_SHIFT,
+					byte_count >> SECTOR_SHIFT,
+					GFP_NOFS, 0);
+		}
+
+		if (unlikely(err != 0)) {
+			printk(KERN_ERR "JBD2: (error %d) unable to wipe journal at physical blocks %llu - %llu",
+					err, block_start, block_stop);
+			return err;
+		}
+
+		block_start = phys_block;
+		block_stop = phys_block;

Is this right?  When we initialized the loop, above, block_stop was
set to block_start-1 (where block_start == phys_block).  So I think it
might be more correct to replace the above two lines with:

		block_start = ~((unsigned long long) 0);

... and then let block_start and block_stop be initialized in a single
place.  Do you agree?  Does this make sense to you?

I just tried this and it actually wouldn't work with this setup because
phys_block would be set after the new call to bmap instead of keeping the value
from the end of the prior loop. However, I have reworked the code using the
general idea of the block_start reset you proposed and I will submit this in
the next version.

Thanks,
Leah

	       	       	    	      	    - Ted