Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757933AbXJXMAZ (ORCPT ); Wed, 24 Oct 2007 08:00:25 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756178AbXJXMAK (ORCPT ); Wed, 24 Oct 2007 08:00:10 -0400 Received: from mail-gw3.sa.ew.hu ([212.108.200.82]:53765 "EHLO mail-gw3.sa.ew.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754355AbXJXMAI (ORCPT ); Wed, 24 Oct 2007 08:00:08 -0400 To: akpm@linux-foundation.org CC: hch@infradead.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: [PATCH] VFS: new fgetattr() file operation Message-Id: From: Miklos Szeredi Date: Wed, 24 Oct 2007 13:59:49 +0200 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4911 Lines: 148 I don't think Christoph will like the patch better, regardless of how I change the description. Of course, I'm open to suggestion on how to improve the interface, but I think fundamentally this is the only way to correctly deal with the below problem. Anyway, here's the patch another time, please consider adding it to -mm. For 2.6.25 obviously. Thanks, Miklos ---- From: Miklos Szeredi Add a new file operation: f_op->fgetattr(), that is invoked by fstat(). Fall back to i_op->getattr() if it is not defined. We need this because fstat() semantics can in some cases be better implemented if the filesystem has the open file available. Let's take the following example: we have a network filesystem, with the server implemented as an unprivileged userspace process running on a UNIX system (this is basically what sshfs does). We want the filesystem to follow the familiar UNIX file semantics as closely as possible. If for example we have this sequence of events, we still would like fstat to work correctly: 1) file X is opened on client 2) file X is renamed to Y on server 3) fstat() is performed on open file descriptor on client This is only possible if the filesystem server acutally uses fstat() on a file descriptor obtained when the file was opened. Which means, the filesystem client needs a way to get this information from the VFS. Even if we assume, that the remote filesystem never changes, it is difficult to implement open-unlink-fstat semantics correctly in the client, without having this information. Signed-off-by: Miklos Szeredi --- Index: linux/fs/stat.c =================================================================== --- linux.orig/fs/stat.c 2007-10-24 11:59:46.000000000 +0200 +++ linux/fs/stat.c 2007-10-24 11:59:47.000000000 +0200 @@ -55,6 +55,33 @@ int vfs_getattr(struct vfsmount *mnt, st EXPORT_SYMBOL(vfs_getattr); +/* + * Perform getattr on an open file + * + * Fall back to i_op->getattr (or generic_fillattr) if the filesystem + * doesn't define an f_op->fgetattr operation. + */ +static int vfs_fgetattr(struct file *file, struct kstat *stat) +{ + struct vfsmount *mnt = file->f_path.mnt; + struct dentry *dentry = file->f_path.dentry; + struct inode *inode = dentry->d_inode; + int retval; + + retval = security_inode_getattr(mnt, dentry); + if (retval) + return retval; + + if (file->f_op && file->f_op->fgetattr) { + return file->f_op->fgetattr(file, stat); + } else if (inode->i_op->getattr) { + return inode->i_op->getattr(mnt, dentry, stat); + } else { + generic_fillattr(inode, stat); + return 0; + } +} + int vfs_stat_fd(int dfd, char __user *name, struct kstat *stat) { struct nameidata nd; @@ -101,7 +128,7 @@ int vfs_fstat(unsigned int fd, struct ks int error = -EBADF; if (f) { - error = vfs_getattr(f->f_path.mnt, f->f_path.dentry, stat); + error = vfs_fgetattr(f, stat); fput(f); } return error; Index: linux/include/linux/fs.h =================================================================== --- linux.orig/include/linux/fs.h 2007-10-24 11:59:46.000000000 +0200 +++ linux/include/linux/fs.h 2007-10-24 11:59:47.000000000 +0200 @@ -1195,6 +1195,7 @@ struct file_operations { ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t, unsigned int); int (*setlease)(struct file *, long, struct file_lock **); int (*revoke)(struct file *, struct address_space *); + int (*fgetattr)(struct file *, struct kstat *); }; struct inode_operations { Index: linux/fs/fuse/file.c =================================================================== --- linux.orig/fs/fuse/file.c 2007-10-24 11:59:46.000000000 +0200 +++ linux/fs/fuse/file.c 2007-10-24 12:01:00.000000000 +0200 @@ -871,6 +871,17 @@ static int fuse_file_flock(struct file * return err; } +static int fuse_file_fgetattr(struct file *file, struct kstat *stat) +{ + struct inode *inode = file->f_dentry->d_inode; + struct fuse_conn *fc = get_fuse_conn(inode); + + if (!fuse_allow_task(fc, current)) + return -EACCES; + + return fuse_update_attributes(inode, stat, file, NULL); +} + static sector_t fuse_bmap(struct address_space *mapping, sector_t block) { struct inode *inode = mapping->host; @@ -920,6 +931,7 @@ static const struct file_operations fuse .fsync = fuse_fsync, .lock = fuse_file_lock, .flock = fuse_file_flock, + .fgetattr = fuse_file_fgetattr, .splice_read = generic_file_splice_read, }; @@ -933,6 +945,7 @@ static const struct file_operations fuse .fsync = fuse_fsync, .lock = fuse_file_lock, .flock = fuse_file_flock, + .fgetattr = fuse_file_fgetattr, /* no mmap and splice_read */ }; - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/