Subject: Re: [PATCH] 9p: Don't use ATTR_* values from fs.h in userspace facing structs

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Sun, 18 Dec 2011 14:08:50 +0530

On Sat, 17 Dec 2011 17:47:25 +0000, Al Viro <[email-masked]> wrote:
> On Sat, Dec 17, 2011 at 05:07:02PM +0200, Sasha Levin wrote:
> > struct p9_iattr_dotl is userspace facing, but the 'valid' field is documented
> > as follows:
> > 
> > 	 * @valid: bitfield specifying which fields are valid
> > 	 *         same as in struct iattr
> > 
> > Which means that the user has to know about kernel internal ATTR_* values.
> > 
> > On Fri, 2011-12-16 at 23:30 +0000, Al Viro wrote:
> > > They *are* kernel internal values and 9P is asking for trouble exposing
> > > them.  Translation: tomorrow we might reassign those as we bloody wish
> > > and any userland code that happens to rely on their values will break.
> > > At which point we'll handle complaints by pointing and laughing.
> > >
> > > It's a 9P bug; fix it there.  Turning random internal constants into a part
> > > of ABI is not going to work.
> > 
> > Signed-off-by: Sasha Levin <[email-masked]>
> > ---
> >  fs/9p/vfs_inode_dotl.c |   31 ++++++++++++++++++++++++++++++-
> >  include/net/9p/9p.h    |   18 ++++++++++++++++++
> >  2 files changed, 48 insertions(+), 1 deletions(-)
> > 
> > diff --git a/fs/9p/vfs_inode_dotl.c b/fs/9p/vfs_inode_dotl.c
> > index 0b5745e..a948214 100644
> > --- a/fs/9p/vfs_inode_dotl.c
> > +++ b/fs/9p/vfs_inode_dotl.c
> > @@ -523,6 +523,35 @@ v9fs_vfs_getattr_dotl(struct vfsmount *mnt, struct dentry *dentry,
> >  	return 0;
> >  }
> >  
> > +int v9fs_vfs_iattr_to_9p_valid(u32 ia_valid)
> > +{
> > +	u32 valid = 0, i;
> > +	static u32 attr_map[][2] = {
> > +		{ATTR_MODE,		P9_ATTR_MODE},
> > +		{ATTR_UID,		P9_ATTR_UID},
> > +		{ATTR_SIZE,		P9_ATTR_SIZE},
> > +		{ATTR_ATIME,		P9_ATTR_ATIME},
> > +		{ATTR_MTIME,		P9_ATTR_MTIME},
> > +		{ATTR_CTIME,		P9_ATTR_CTIME},
> > +		{ATTR_ATIME_SET,	P9_ATTR_ATIME_SET},
> > +		{ATTR_MTIME_SET,	P9_ATTR_MTIME_SET},
> > +		{ATTR_FORCE,		P9_ATTR_FORCE},
> > +		{ATTR_ATTR_FLAG,	P9_ATTR_ATTR_FLAG},
> > +		{ATTR_KILL_SUID,	P9_ATTR_KILL_SUID},
> > +		{ATTR_KILL_SGID,	P9_ATTR_KILL_SGID},
> > +		{ATTR_FILE,		P9_ATTR_FILE},
> > +		{ATTR_KILL_PRIV,	P9_ATTR_KILL_PRIV},
> > +		{ATTR_OPEN,		P9_ATTR_OPEN},
> > +		{ATTR_TIMES_SET,	P9_ATTR_TIMES_SET},
> > +	};
> 
> a) ATTR_GID is lost
> b) passing ATTR_FILE is bloody pointless; look at what it does and
> realize that 9p doesn't as much as look at ia_file.
> c) ATTR_KILL_PRIV is very dubious; what's the legitimate use of that
> puppy in fs code?
> 
> Look, that's the problem with exposing this stuff to protocol; you don't
> get clear semantics and are you seriously asking for trouble on kernel
> changes.  Suppose tomorrow we get rid of e.g. ATTR_KILL_PRIV; what are you
> guys going to do?  Hope that no 9p server has behaviour dependent on that
> flag being set or cleared?
> 
> Don't turn the kernel internals into a part of ABI.  And blind bulk remapping
> of constants is exactly that...
> 

I am testing this locally.

commit 8ebbbcf5185096acccc523fb040e770d7876d4cd
Author: Aneesh Kumar K.V <[email-masked]>
Date:   Sat Dec 17 21:01:08 2011 +0530

    fs/9p: iattr_valid flags are kernel internal flags map them to 9p values.
    
    Kernel internal values can change, add protocol values for these constant and
    use them.
    
    Signed-off-by: Aneesh Kumar K.V <[email-masked]>

diff --git a/fs/9p/vfs_inode_dotl.c b/fs/9p/vfs_inode_dotl.c
index 0b5745e..a81808a 100644
--- a/fs/9p/vfs_inode_dotl.c
+++ b/fs/9p/vfs_inode_dotl.c
@@ -523,6 +523,46 @@ v9fs_vfs_getattr_dotl(struct vfsmount *mnt, struct dentry *dentry,
 	return 0;
 }
 
+/*
+ * Attribute flags.
+ */
+#define P9_ATTR_MODE		(1 << 0)
+#define P9_ATTR_UID		(1 << 1)
+#define P9_ATTR_GID		(1 << 2)
+#define P9_ATTR_SIZE		(1 << 3)
+#define P9_ATTR_ATIME		(1 << 4)
+#define P9_ATTR_MTIME		(1 << 5)
+#define P9_ATTR_CTIME		(1 << 6)
+#define P9_ATTR_ATIME_SET	(1 << 7)
+#define P9_ATTR_MTIME_SET	(1 << 8)
+
+struct dotl_iattr_map {
+	int iattr_valid;
+	int p9_iattr_valid;
+};
+
+static int v9fs_mapped_iattr_valid(int iattr_valid)
+{
+	int i;
+	int p9_iattr_valid = 0;
+	struct dotl_iattr_map dotl_iattr_map[] = {
+		{ ATTR_MODE,		P9_ATTR_MODE },
+		{ ATTR_UID,		P9_ATTR_UID },
+		{ ATTR_GID,		P9_ATTR_GID },
+		{ ATTR_SIZE,		P9_ATTR_SIZE },
+		{ ATTR_ATIME,		P9_ATTR_ATIME },
+		{ ATTR_MTIME,		P9_ATTR_MTIME },
+		{ ATTR_CTIME,		P9_ATTR_CTIME },
+		{ ATTR_ATIME_SET,	P9_ATTR_ATIME_SET },
+		{ ATTR_MTIME_SET,	P9_ATTR_MTIME_SET },
+	};
+	for (i = 0; i < ARRAY_SIZE(dotl_iattr_map); i++) {
+		if (iattr_valid & dotl_iattr_map[i].iattr_valid)
+			p9_iattr_valid |= dotl_iattr_map[i].p9_iattr_valid;
+	}
+	return p9_iattr_valid;
+}
+
 /**
  * v9fs_vfs_setattr_dotl - set file metadata
  * @dentry: file whose metadata to set
@@ -543,7 +583,7 @@ int v9fs_vfs_setattr_dotl(struct dentry *dentry, struct iattr *iattr)
 	if (retval)
 		return retval;
 
-	p9attr.valid = iattr->ia_valid;
+	p9attr.valid = v9fs_mapped_iattr_valid(iattr->ia_valid);
 	p9attr.mode = iattr->ia_mode;
 	p9attr.uid = iattr->ia_uid;
 	p9attr.gid = iattr->ia_gid;