cifs: add support for FALLOC_FL_COLLAPSE_RANGE

Emulated for SMB3 and later via server side copy
and setsize. Eventually this could be compounded.
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/smb2ops.c

@@ -3688,6 +3688,39 @@ static long smb3_simple_falloc(struct file *file, struct cifs_tcon *tcon,
 	return rc;
 }
 
+static long smb3_collapse_range(struct file *file, struct cifs_tcon *tcon,
+			    loff_t off, loff_t len)
+{
+	int rc;
+	unsigned int xid;
+	struct cifsFileInfo *cfile = file->private_data;
+	__le64 eof;
+
+	xid = get_xid();
+
+	if (off >= i_size_read(file->f_inode) ||
+	    off + len >= i_size_read(file->f_inode)) {
+		rc = -EINVAL;
+		goto out;
+	}
+
+	rc = smb2_copychunk_range(xid, cfile, cfile, off + len,
+				  i_size_read(file->f_inode) - off - len, off);
+	if (rc < 0)
+		goto out;
+
+	eof = cpu_to_le64(i_size_read(file->f_inode) - len);
+	rc = SMB2_set_eof(xid, tcon, cfile->fid.persistent_fid,
+			  cfile->fid.volatile_fid, cfile->pid, &eof);
+	if (rc < 0)
+		goto out;
+
+	rc = 0;
+ out:
+	free_xid(xid);
+	return rc;
+}
+
 static loff_t smb3_llseek(struct file *file, struct cifs_tcon *tcon, loff_t offset, int whence)
 {
 	struct cifsFileInfo *wrcfile, *cfile = file->private_data;
@@ -3859,6 +3892,8 @@ static long smb3_fallocate(struct file *file, struct cifs_tcon *tcon, int mode,
 		return smb3_zero_range(file, tcon, off, len, false);
 	} else if (mode == FALLOC_FL_KEEP_SIZE)
 		return smb3_simple_falloc(file, tcon, off, len, true);
+	else if (mode == FALLOC_FL_COLLAPSE_RANGE)
+		return smb3_collapse_range(file, tcon, off, len);
 	else if (mode == 0)
 		return smb3_simple_falloc(file, tcon, off, len, false);