On Thu, 2011-01-20 at 04:41 +0800, Andrew Morton wrote: > On Wed, 19 Jan 2011 09:15:18 +0800 > Shaohua Li <[email protected]> wrote: > > > Subject: add metadata_incore ioctl in vfs > > > > Add an ioctl to dump filesystem's metadata in memory in vfs. Userspace > > collects > > such info and uses it to do metadata readahead. > > Filesystem can hook to super_operations.metadata_incore to get metadata in > > specific approach. Next patch will give an example how to implement > > .metadata_incore in btrfs. > > > > ... > > > > /* > > + * Copy info about metadata in memory to userspace > > + * Returns: > > + * = 1, one metadata range copied to userspace > > + * = 0, no more metadata > > + * < 0, error > > + */ > > +static int ioctl_metadata_incore(struct file *filp, void __user *argp) > > +{ > > + struct super_block *sb = filp->f_path.dentry->d_inode->i_sb; > > + struct metadata_incore_args args; > > + loff_t offset; > > + ssize_t size; > > + > > + if (!sb->s_op->metadata_incore) > > + return -EINVAL; > > + > > + if (copy_from_user(&args, argp, sizeof(args))) > > + return -EFAULT; > > + > > + /* we check metadata info in page unit */ > > + if (args.offset & ~PAGE_CACHE_MASK) > > + return -EINVAL; > > + > > + offset = args.offset; > > + > > + if (sb->s_op->metadata_incore(sb, &offset, &size) < 0) > > + return 0; > > + > > + args.address = offset; > > + args.size = size; > > + args.unused = 0; > > + > > + if (copy_to_user(argp, &args, sizeof(args))) > > + return -EFAULT; > > + > > + return 1; > > +} > > So userspace opens any file on the fs and runs this ioctl against it? > > That's a pretty awkward interface - we're doing an fs-wide operation > but the fs is identified by a single file which happens to live on that > fs. For example, this precludes a future extension whereby userspace > can query the incore metadata for a particular file. The statfs > syscall sucks in the same manner. > > I don't know if this is worth addressing. Perhaps require that the > filp refers to the root of the fs? I didn't see why this is needed, but I can limit the fip to the root of the fs.
> Also, is this a privileged operation? If not, then that might be a > problem - could it be used by unprivileged users to work out which > files have been opened recently or something like that? it's harmless even a unprivileged user uses it. I don't think unprivileged user can decode the data returned from the ioctl. Thanks, Shaohua -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
