On Mon, May 11, 2009 at 11:08:56PM -0400, Theodore Tso wrote: > On Thu, May 07, 2009 at 04:09:29PM +0530, Aneesh Kumar K.V wrote: > > ext4_get_blocks_wrap does a block lookup requesting to > > allocate new blocks. A lookup of blocks in prealloc area > > result in setting the unwritten flag in buffer_head. So > > a write to an unwritten extent will cause the buffer_head > > to have unwritten and mapped flag set. Clear hte unwritten > > buffer_head flag before requesting to allocate blocks. > > > > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx> > > I've rewritten the commit changelog to this, which I believe more > accurately describes the patch. Comments, please? > > ext4: Clear the unwritten buffer_head flag after the extent is initialized > > From: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx> > > The BH_Unwritten flag indicates that the buffer is allocated on disk > but has not been written; that is, the disk was part of a persistent > preallocation area. That flag should only be set when a get_blocks() > function is looking up a inode's logical to physical block mapping. > > When ext4_get_blocks_wrap() is called with create=1, the uninitialized > extent is converted into an initialized one, so the BH_Unwritten flag > is no longer appropriate. Hence, we need to make sure the > BH_Unwritten is not left set, to avoid the ensuing confusion and > hilarty. > > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx> > Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx> > I think it is good. But one thing missing in the commit message is, what happens if we do a write to prealloc space. Since a get_block(create = 1) is now split into __get_block(create = 0 ) and __get_block(create = 1). That would mean if we pass a buffer head with BH_Unwritten cleared we will have 1) buffer_head as BH_Unwritten cleared. 2) __get_block(create = 0 ) -> Since it is prealloc space we will have BH_Unwritten set . 3) __get_block(create = 1) -> get the blocks out of prealloc space. and retun with BH_Mapped set. That would imply we have BH_Unwritten and BH_Mapped set in the above case which is wrong. So we need a BH_Unwritten clear between (2) and (3). The patch does the same. May be we need to capture it in commit message. -aneesh -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
