Re: [PATCH 6/9] f2fs: zstd: Switch to the zstd-1.4.6 API

From: Chao Yu
Date: Thu Sep 17 2020 - 22:58:50 EST

On 2020/9/18 10:56, Eric Biggers wrote:
On Fri, Sep 18, 2020 at 09:47:32AM +0800, Chao Yu wrote:
Ah, I got it.

Step of enabling compressed inode is not correct, we should touch an empty
file, and then use 'chattr +c' on that file to enable compression, otherwise
the race condition could be complicated to handle. So we need below diff to
disallow setting compression flag on an non-empty file:

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 8a422400e824..b462db7898fd 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -1836,6 +1836,8 @@ static int f2fs_setflags_common(struct inode *inode, u32 iflags, u32 mask)
if (iflags & F2FS_COMPR_FL) {
if (!f2fs_may_compress(inode))
return -EINVAL;
+ if (get_dirty_pages(inode) || fi->i_compr_blocks)
+ return -EINVAL;


Why not:

if (inode->i_size)
return -EINVAL;

Yeah, I noticed that after replying this email, I've prepared the new patch
which including the i_size check.

Thanks for noticing this.