[RFC PATCH 1/2] 9p: retrieve fid from file when file instance exist.

[Jianyong Wu]

In the current setattr implementation in 9p, fid will always retrieved from
dentry no matter file instance exist or not when setattr. There will
be some info related to open file instance dropped. so it's better
to retrieve fid from file instance if file instance is passed to setattr.

for example:
fd=open("tmp", O_RDWR);
ftruncate(fd, 10);

the file context related with fd info will lost as fid will always be
retrieved from dentry, then the backend can't get the info of file context.
it is against the original intention of user and may lead to bug.

Signed-off-by: Jianyong Wu <jianyong.wu@xxxxxxx>
---
 fs/9p/vfs_inode.c      | 5 ++++-
 fs/9p/vfs_inode_dotl.c | 5 ++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/9p/vfs_inode.c b/fs/9p/vfs_inode.c
index c9255d399917..010869389523 100644
--- a/fs/9p/vfs_inode.c
+++ b/fs/9p/vfs_inode.c
@@ -1100,7 +1100,10 @@ static int v9fs_vfs_setattr(struct dentry *dentry, struct iattr *iattr)
 
 	retval = -EPERM;
 	v9ses = v9fs_dentry2v9ses(dentry);
-	fid = v9fs_fid_lookup(dentry);
+	if (iattr->ia_valid & ATTR_FILE)
+		fid = iattr->ia_file->private_data;
+	else
+		fid = v9fs_fid_lookup(dentry);
 	if(IS_ERR(fid))
 		return PTR_ERR(fid);
 
diff --git a/fs/9p/vfs_inode_dotl.c b/fs/9p/vfs_inode_dotl.c
index 60328b21c5fb..28fb04cbeb1a 100644
--- a/fs/9p/vfs_inode_dotl.c
+++ b/fs/9p/vfs_inode_dotl.c
@@ -560,7 +560,10 @@ int v9fs_vfs_setattr_dotl(struct dentry *dentry, struct iattr *iattr)
 	p9attr.mtime_sec = iattr->ia_mtime.tv_sec;
 	p9attr.mtime_nsec = iattr->ia_mtime.tv_nsec;
 
-	fid = v9fs_fid_lookup(dentry);
+	if (iattr->ia_valid & ATTR_FILE)
+		fid = iattr->ia_file->private_data;
+	else
+		fid = v9fs_fid_lookup(dentry);
 	if (IS_ERR(fid))
 		return PTR_ERR(fid);
 
-- 
2.17.1