linux-ext4 - Re: [PATCH 1/4] e2fsprogs: Add undo I/O manager

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Date:	Fri, 03 Aug 2007 00:02:32 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Andreas Dilger <adilger@...sterfs.com>
CC:	tytso@....edu, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 1/4] e2fsprogs: Add undo I/O manager



Andreas Dilger wrote:
> On Aug 01, 2007  21:04 +0530, Aneesh Kumar K.V wrote:
>> +static errcode_t write_file_system_identity(io_channel undo_channel,
>> +							TDB_CONTEXT *tdb)
>> +{
>> +	/* Write to tdb file in the file system byte order */
>> +	tdb_key.dptr = "filesystem MTIME";
>> +	tdb_key.dsize = sizeof("filesystem MTIME");
>> +	tdb_data.dptr = (unsigned char *) &(super.s_mtime);
>> +	tdb_data.dsize = sizeof(super.s_mtime);
>> +
>> +	tdb_key.dptr = "filesystem UUID";
>> +	tdb_key.dsize = sizeof("filesystem UUID");
>> +	tdb_data.dptr = (unsigned char *)&(super.s_uuid);
>> +	tdb_data.dsize = sizeof(super.s_uuid);
> 
> Is this the mtime and UUID of the new filesystem or the old one?  It
> should be the UUID and mtime of the new filesystem, so that the
> undo file can be verified against the current superblock.  This poses
> a bit of a problem, because that information isn't saved until after
> the mke2fs run is finished.
> 
> One possibility is to overwrite this information at the end of mke2fs
> after the new UUID and mtime are written?
> 

This can be done by writing the file system identity during the the io_channel_close.
How about this patch on top of the last series. I will merge this into the patcheset

diff --git a/lib/ext2fs/undo_io.c b/lib/ext2fs/undo_io.c
index 30e2514..a80bafc 100644
--- a/lib/ext2fs/undo_io.c
+++ b/lib/ext2fs/undo_io.c
@@ -159,8 +159,8 @@ static errcode_t write_file_system_identity(io_channel undo_channel,
 	/* Also store the block size */
 	tdb_key.dptr = "filesystem BLKSIZE";
 	tdb_key.dsize = sizeof("filesystem BLKSIZE");
-	tdb_data.dptr = (unsigned char *)&(undo_channel->block_size);
-	tdb_data.dsize = sizeof(undo_channel->block_size);
+	tdb_data.dptr = (unsigned char *)&(tdb_data_size);
+	tdb_data.dsize = sizeof(tdb_data_size);
 
 	retval = tdb_store(tdb, tdb_key, tdb_data, TDB_INSERT);
 	if (retval == -1) {
@@ -199,13 +199,6 @@ static errcode_t undo_write_tdb(io_channel channel,
 	 */
 	if (!tdb_data_size) {
 		tdb_data_size = channel->block_size;
-
-		/*
-		 * First write. Write the file system identity
-		 */
-		retval = write_file_system_identity(channel, data->tdb);
-		if (retval)
-			return retval;
 	}
 
 	if (count == 1)
@@ -405,6 +398,11 @@ static errcode_t undo_close(io_channel channel)
 	if (--channel->refcount > 0)
 		return 0;
 
+	/* Before closing Write the file system identity */
+	retval = write_file_system_identity(channel, data->tdb);
+	if (retval)
+		return retval;
+
 	if (data->real)
 		retval = io_channel_close(data->real);
 
-
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