GFS2: Add atomic_open support

I've restricted atomic_open to only operate on regular files, although
I still don't understand why atomic_open should not be possible also for
directories on GFS2. That can always be added in later though, if it
makes sense.

The ->atomic_open function can be passed negative dentries, which
in most cases means either ENOENT (->lookup) or a call to d_instantiate
(->create). In the GFS2 case though, we need to actually perform the
look up, since we do not know whether there has been a new inode created
on another node. The look up calls d_splice_alias which then tries to
rehash the dentry - so the solution here is to simply check for that
in d_splice_alias. The same issue is likely to affect any other cluster
filesystem implementing ->atomic_open

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: "J. Bruce Fields" <bfields fieldses org>
Cc: Jeff Layton <jlayton@redhat.com>

3 files changed, 146 insertions, 49 deletions

diff --git a/fs/gfs2/file.c b/fs/gfs2/file.c
index ad0dc38d87ab..4ed6a03e565b 100644
--- a/fs/gfs2/file.c
+++ b/fs/gfs2/file.c
@@ -538,21 +538,30 @@ static int gfs2_mmap(struct file *file, struct vm_area_struct *vma)
 }
 
 /**
- * gfs2_open - open a file
- * @inode: the inode to open
- * @file: the struct file for this opening
+ * gfs2_open_common - This is common to open and atomic_open
+ * @inode: The inode being opened
+ * @file: The file being opened
  *
- * Returns: errno
+ * This maybe called under a glock or not depending upon how it has
+ * been called. We must always be called under a glock for regular
+ * files, however. For other file types, it does not matter whether
+ * we hold the glock or not.
+ *
+ * Returns: Error code or 0 for success
  */
 
-static int gfs2_open(struct inode *inode, struct file *file)
+int gfs2_open_common(struct inode *inode, struct file *file)
 {
-        struct gfs2_inode *ip = GFS2_I(inode);
-        struct gfs2_holder i_gh;
         struct gfs2_file *fp;
-        int error;
+        int ret;
 
-        fp = kzalloc(sizeof(struct gfs2_file), GFP_KERNEL);
+        if (S_ISREG(inode->i_mode)) {
+                ret = generic_file_open(inode, file);
+                if (ret)
+                        return ret;
+        }
+
+        fp = kzalloc(sizeof(struct gfs2_file), GFP_NOFS);
         if (!fp)
                 return -ENOMEM;
 
@@ -560,29 +569,43 @@ static int gfs2_open(struct inode *inode, struct file *file)
 
         gfs2_assert_warn(GFS2_SB(inode), !file->private_data);
         file->private_data = fp;
+        return 0;
+}
+
+/**
+ * gfs2_open - open a file
+ * @inode: the inode to open
+ * @file: the struct file for this opening
+ *
+ * After atomic_open, this function is only used for opening files
+ * which are already cached. We must still get the glock for regular
+ * files to ensure that we have the file size uptodate for the large
+ * file check which is in the common code. That is only an issue for
+ * regular files though.
+ *
+ * Returns: errno
+ */
+
+static int gfs2_open(struct inode *inode, struct file *file)
+{
+        struct gfs2_inode *ip = GFS2_I(inode);
+        struct gfs2_holder i_gh;
+        int error;
+        bool need_unlock = false;
 
         if (S_ISREG(ip->i_inode.i_mode)) {
                 error = gfs2_glock_nq_init(ip->i_gl, LM_ST_SHARED, LM_FLAG_ANY,
                                            &i_gh);
                 if (error)
-                        goto fail;
+                        return error;
+                need_unlock = true;
+        }
 
-                if (!(file->f_flags & O_LARGEFILE) &&
-                    i_size_read(inode) > MAX_NON_LFS) {
-                        error = -EOVERFLOW;
-                        goto fail_gunlock;
-                }
+        error = gfs2_open_common(inode, file);
 
+        if (need_unlock)
                 gfs2_glock_dq_uninit(&i_gh);
-        }
-
-        return 0;
 
-fail_gunlock:
-        gfs2_glock_dq_uninit(&i_gh);
-fail:
-        file->private_data = NULL;
-        kfree(fp);
         return error;
 }
 
diff --git a/fs/gfs2/inode.c b/fs/gfs2/inode.c
index ede16ae784e2..bbb2715171cd 100644
--- a/fs/gfs2/inode.c
+++ b/fs/gfs2/inode.c
@@ -535,6 +535,7 @@ static int gfs2_security_init(struct gfs2_inode *dip, struct gfs2_inode *ip,
  * gfs2_create_inode - Create a new inode
  * @dir: The parent directory
  * @dentry: The new dentry
+ * @file: If non-NULL, the file which is being opened
  * @mode: The permissions on the new inode
  * @dev: For device nodes, this is the device number
  * @symname: For symlinks, this is the link destination
@@ -544,8 +545,9 @@ static int gfs2_security_init(struct gfs2_inode *dip, struct gfs2_inode *ip,
  */
 
 static int gfs2_create_inode(struct inode *dir, struct dentry *dentry,
+                             struct file *file,
                              umode_t mode, dev_t dev, const char *symname,
-                             unsigned int size, int excl)
+                             unsigned int size, int excl, int *opened)
 {
         const struct qstr *name = &dentry->d_name;
         struct gfs2_holder ghs[2];
@@ -553,6 +555,7 @@ static int gfs2_create_inode(struct inode *dir, struct dentry *dentry,
         struct gfs2_inode *dip = GFS2_I(dir), *ip;
         struct gfs2_sbd *sdp = GFS2_SB(&dip->i_inode);
         struct gfs2_glock *io_gl;
+        struct dentry *d;
         int error;
         u32 aflags = 0;
         int arq;
@@ -579,9 +582,20 @@ static int gfs2_create_inode(struct inode *dir, struct dentry *dentry,
         inode = gfs2_dir_search(dir, &dentry->d_name, !S_ISREG(mode) || excl);
         error = PTR_ERR(inode);
         if (!IS_ERR(inode)) {
+                d = d_splice_alias(inode, dentry);
+                error = 0;
+                if (file && !IS_ERR(d)) {
+                        if (d == NULL)
+                                d = dentry;
+                        if (S_ISREG(inode->i_mode))
+                                error = finish_open(file, d, gfs2_open_common, opened);
+                        else
+                                error = finish_no_open(file, d);
+                }
                 gfs2_glock_dq_uninit(ghs);
-                d_instantiate(dentry, inode);
-                return 0;
+                if (IS_ERR(d))
+                        return PTR_RET(d);
+                return error;
         } else if (error != -ENOENT) {
                 goto fail_gunlock;
         }
@@ -679,10 +693,12 @@ static int gfs2_create_inode(struct inode *dir, struct dentry *dentry,
                 goto fail_gunlock3;
 
         mark_inode_dirty(inode);
+        d_instantiate(dentry, inode);
+        if (file)
+                error = finish_open(file, dentry, gfs2_open_common, opened);
         gfs2_glock_dq_uninit(ghs);
         gfs2_glock_dq_uninit(ghs + 1);
-        d_instantiate(dentry, inode);
-        return 0;
+        return error;
 
 fail_gunlock3:
         gfs2_glock_dq_uninit(ghs + 1);
@@ -722,36 +738,56 @@ fail:
 static int gfs2_create(struct inode *dir, struct dentry *dentry,
                        umode_t mode, bool excl)
 {
-        return gfs2_create_inode(dir, dentry, S_IFREG | mode, 0, NULL, 0, excl);
+        return gfs2_create_inode(dir, dentry, NULL, S_IFREG | mode, 0, NULL, 0, excl, NULL);
 }
 
 /**
- * gfs2_lookup - Look up a filename in a directory and return its inode
+ * __gfs2_lookup - Look up a filename in a directory and return its inode
  * @dir: The directory inode
  * @dentry: The dentry of the new inode
- * @nd: passed from Linux VFS, ignored by us
+ * @file: File to be opened
+ * @opened: atomic_open flags
  *
- * Called by the VFS layer. Lock dir and call gfs2_lookupi()
  *
  * Returns: errno
  */
 
-static struct dentry *gfs2_lookup(struct inode *dir, struct dentry *dentry,
-                                  unsigned int flags)
+static struct dentry *__gfs2_lookup(struct inode *dir, struct dentry *dentry,
+                                    struct file *file, int *opened)
 {
-        struct inode *inode = gfs2_lookupi(dir, &dentry->d_name, 0);
-        if (inode && !IS_ERR(inode)) {
-                struct gfs2_glock *gl = GFS2_I(inode)->i_gl;
-                struct gfs2_holder gh;
-                int error;
-                error = gfs2_glock_nq_init(gl, LM_ST_SHARED, LM_FLAG_ANY, &gh);
-                if (error) {
-                        iput(inode);
-                        return ERR_PTR(error);
-                }
-                gfs2_glock_dq_uninit(&gh);
+        struct inode *inode;
+        struct dentry *d;
+        struct gfs2_holder gh;
+        struct gfs2_glock *gl;
+        int error;
+
+        inode = gfs2_lookupi(dir, &dentry->d_name, 0);
+        if (!inode)
+                return NULL;
+        if (IS_ERR(inode))
+                return ERR_CAST(inode);
+
+        gl = GFS2_I(inode)->i_gl;
+        error = gfs2_glock_nq_init(gl, LM_ST_SHARED, LM_FLAG_ANY, &gh);
+        if (error) {
+                iput(inode);
+                return ERR_PTR(error);
         }
-        return d_splice_alias(inode, dentry);
+
+        d = d_splice_alias(inode, dentry);
+        if (file && S_ISREG(inode->i_mode))
+                error = finish_open(file, dentry, gfs2_open_common, opened);
+
+        gfs2_glock_dq_uninit(&gh);
+        if (error)
+                return ERR_PTR(error);
+        return d;
+}
+
+static struct dentry *gfs2_lookup(struct inode *dir, struct dentry *dentry,
+                                  unsigned flags)
+{
+        return __gfs2_lookup(dir, dentry, NULL, NULL);
 }
 
 /**
@@ -1069,7 +1105,7 @@ static int gfs2_symlink(struct inode *dir, struct dentry *dentry,
         if (size > sdp->sd_sb.sb_bsize - sizeof(struct gfs2_dinode) - 1)
                 return -ENAMETOOLONG;
 
-        return gfs2_create_inode(dir, dentry, S_IFLNK | S_IRWXUGO, 0, symname, size, 0);
+        return gfs2_create_inode(dir, dentry, NULL, S_IFLNK | S_IRWXUGO, 0, symname, size, 0, NULL);
 }
 
 /**
@@ -1085,7 +1121,7 @@ static int gfs2_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
 {
         struct gfs2_sbd *sdp = GFS2_SB(dir);
         unsigned dsize = sdp->sd_sb.sb_bsize - sizeof(struct gfs2_dinode);
-        return gfs2_create_inode(dir, dentry, S_IFDIR | mode, 0, NULL, dsize, 0);
+        return gfs2_create_inode(dir, dentry, NULL, S_IFDIR | mode, 0, NULL, dsize, 0, NULL);
 }
 
 /**
@@ -1100,7 +1136,43 @@ static int gfs2_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
 static int gfs2_mknod(struct inode *dir, struct dentry *dentry, umode_t mode,
                       dev_t dev)
 {
-        return gfs2_create_inode(dir, dentry, mode, dev, NULL, 0, 0);
+        return gfs2_create_inode(dir, dentry, NULL, mode, dev, NULL, 0, 0, NULL);
+}
+
+/**
+ * gfs2_atomic_open - Atomically open a file
+ * @dir: The directory
+ * @dentry: The proposed new entry
+ * @file: The proposed new struct file
+ * @flags: open flags
+ * @mode: File mode
+ * @opened: Flag to say whether the file has been opened or not
+ *
+ * Returns: error code or 0 for success
+ */
+
+static int gfs2_atomic_open(struct inode *dir, struct dentry *dentry,
+                            struct file *file, unsigned flags,
+                            umode_t mode, int *opened)
+{
+        struct dentry *d;
+        bool excl = !!(flags & O_EXCL);
+
+        d = __gfs2_lookup(dir, dentry, file, opened);
+        if (IS_ERR(d))
+                return PTR_ERR(d);
+        if (d == NULL)
+                d = dentry;
+        if (d->d_inode) {
+                if (!(*opened & FILE_OPENED))
+                        return finish_no_open(file, d);
+                return 0;
+        }
+
+        if (!(flags & O_CREAT))
+                return -ENOENT;
+
+        return gfs2_create_inode(dir, dentry, file, S_IFREG | mode, 0, NULL, 0, excl, opened);
 }
 
 /*
@@ -1780,6 +1852,7 @@ const struct inode_operations gfs2_dir_iops = {
         .removexattr = gfs2_removexattr,
         .fiemap = gfs2_fiemap,
         .get_acl = gfs2_get_acl,
+        .atomic_open = gfs2_atomic_open,
 };
 
 const struct inode_operations gfs2_symlink_iops = {
diff --git a/fs/gfs2/inode.h b/fs/gfs2/inode.h
index c53c7477f6da..ba4d9492d422 100644
--- a/fs/gfs2/inode.h
+++ b/fs/gfs2/inode.h
@@ -109,6 +109,7 @@ extern int gfs2_permission(struct inode *inode, int mask);
 extern int gfs2_setattr_simple(struct inode *inode, struct iattr *attr);
 extern struct inode *gfs2_lookup_simple(struct inode *dip, const char *name);
 extern void gfs2_dinode_out(const struct gfs2_inode *ip, void *buf);
+extern int gfs2_open_common(struct inode *inode, struct file *file);
 
 extern const struct inode_operations gfs2_file_iops;
 extern const struct inode_operations gfs2_dir_iops;