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Message-ID: <20080822181458.GA15469@infradead.org> Date: Fri, 22 Aug 2008 14:14:58 -0400 From: Christoph Hellwig <hch@...radead.org> To: Takashi Sato <t-sato@...jp.nec.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>, "dm-devel@...hat.com" <dm-devel@...hat.com>, "viro@...IV.linux.org.uk" <viro@...IV.linux.org.uk>, "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>, "xfs@....sgi.com" <xfs@....sgi.com>, Christoph Hellwig <hch@...radead.org>, "axboe@...nel.dk" <axboe@...nel.dk>, "mtk.manpages@...glemail.com" <mtk.manpages@...glemail.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH 1/3] Implement generic freeze feature On Mon, Aug 18, 2008 at 09:28:19PM +0900, Takashi Sato wrote: > + down(&bdev->bd_freeze_sem); > + bdev->bd_freeze_count++; > + if (bdev->bd_freeze_count > 1) { > + sb = get_super(bdev); > + drop_super(sb); > + up(&bdev->bd_freeze_sem); > + return sb; > + } > + > down(&bdev->bd_mount_sem); Now you have a reference counter of freezes which actually is pretty sensible, but also needs some documentation. What I don't understand here at all is why you do the get_super/drop_super in the already frozen case. Now that the freeze_count has replaced one of the uses of bd_mount_sem you should also replace the other use in the unmount path by simply checking for the freez_count and abort if it's set. To do so you'll need to hold the bd_mount_sem over the whole unmount operation to prevent new frezes from coming in. As others noted it should be a mutex and not a semaphore. > /* > + * ioctl_freeze - Freeze the filesystem. > + * > + * @filp: target file > + * > + * Call freeze_bdev() to freeze the filesystem. > + */ > +static int ioctl_freeze(struct file *filp) This is not quite kerneldcoc format, which would ne a /** as commnt start. But I don't think the comment is actually needed, it's a pretty obvious file scope function. (Same commnt also applies to ioctl_thaw) > + struct super_block *sb = filp->f_path.dentry->d_inode->i_sb; > + > + if (!capable(CAP_SYS_ADMIN)) > + return -EPERM; > + > + /* If filesystem doesn't support freeze feature, return. */ > + if (sb->s_op->write_super_lockfs == NULL) > + return -EOPNOTSUPP; > + > + /* If a regular file or a directory isn't specified, return. */ > + if (sb->s_bdev == NULL) > + return -EINVAL; I don't understand this commnt. What you are checking is that the filesystem has a non-NULL s_bdev, which implies a not blockdevice-backed filesystem. -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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