linux-kernel - [PATCH] pipe: export size and blocks via system call fstat(2)

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Message-Id: <1274969391-3006-1-git-send-email-xiaosuo@gmail.com>
Date:	Thu, 27 May 2010 22:09:51 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	Alexander Viro <viro@...iv.linux.org.uk>
Cc:	Matthew Wilcox <matthew@....cx>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, Changli Gao <xiaosuo@...il.com>
Subject: [PATCH] pipe: export size and blocks via system call fstat(2)

export size and blocks via system call fstat(2)

pipe or fifo doesn't support fstat(2). This patch makes it possible to check the
amount of data buffered in a pipe or fifo, and the pages used to store this
data via fstat(2).

Signed-off-by: Changli Gao <xiaosuo@...il.com>
----
 fs/inode.c         |    5 +++--
 fs/pipe.c          |   51 ++++++++++++++++++++++++++++++++++++++++-----------
 include/linux/fs.h |    1 +
 3 files changed, 44 insertions(+), 13 deletions(-)
diff --git a/fs/inode.c b/fs/inode.c
index 258ec22..850ff89 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1598,9 +1598,10 @@ void init_special_inode(struct inode *inode, umode_t mode, dev_t rdev)
 	} else if (S_ISBLK(mode)) {
 		inode->i_fop = &def_blk_fops;
 		inode->i_rdev = rdev;
-	} else if (S_ISFIFO(mode))
+	} else if (S_ISFIFO(mode)) {
+		inode->i_op = &pipe_iops;
 		inode->i_fop = &def_fifo_fops;
-	else if (S_ISSOCK(mode))
+	} else if (S_ISSOCK(mode))
 		inode->i_fop = &bad_sock_fops;
 	else
 		printk(KERN_DEBUG "init_special_inode: bogus i_mode (%o) for"
diff --git a/fs/pipe.c b/fs/pipe.c
index 37ba29f..3961fcf 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -625,25 +625,33 @@ bad_pipe_w(struct file *filp, const char __user *buf, size_t count,
 	return -EBADF;
 }
 
-static long pipe_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
+static int __pipe_get_size(struct inode *inode)
 {
-	struct inode *inode = filp->f_path.dentry->d_inode;
 	struct pipe_inode_info *pipe;
 	int count, buf, nrbufs;
 
+	pipe = inode->i_pipe;
+	count = 0;
+	buf = pipe->curbuf;
+	nrbufs = pipe->nrbufs;
+	while (--nrbufs >= 0) {
+		count += pipe->bufs[buf].len;
+		buf = (buf+1) & (PIPE_BUFFERS-1);
+	}
+
+	return count;
+}
+
+static long pipe_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
+{
+	struct inode *inode = filp->f_path.dentry->d_inode;
+	int count;
+
 	switch (cmd) {
 		case FIONREAD:
 			mutex_lock(&inode->i_mutex);
-			pipe = inode->i_pipe;
-			count = 0;
-			buf = pipe->curbuf;
-			nrbufs = pipe->nrbufs;
-			while (--nrbufs >= 0) {
-				count += pipe->bufs[buf].len;
-				buf = (buf+1) & (PIPE_BUFFERS-1);
-			}
+			count = __pipe_get_size(inode);
 			mutex_unlock(&inode->i_mutex);
-
 			return put_user(count, (int __user *)arg);
 		default:
 			return -EINVAL;
@@ -934,6 +942,7 @@ static struct inode * get_pipe_inode(void)
 	inode->i_pipe = pipe;
 
 	pipe->readers = pipe->writers = 1;
+	inode->i_op = &pipe_iops;
 	inode->i_fop = &rdwr_pipefifo_fops;
 
 	/*
@@ -1112,6 +1121,26 @@ static struct file_system_type pipe_fs_type = {
 	.kill_sb	= kill_anon_super,
 };
 
+static int pipe_getattr(struct vfsmount *mnt, struct dentry *dentry,
+			struct kstat *stat)
+{
+	struct inode *inode = dentry->d_inode;
+
+	generic_fillattr(inode, stat);
+	mutex_lock(&inode->i_mutex);
+	if (inode->i_pipe) {
+		stat->blocks = inode->i_pipe->nrbufs * (PAGE_SIZE / 512);
+		stat->size = __pipe_get_size(inode);
+	}
+	mutex_unlock(&inode->i_mutex);
+
+	return 0;
+}
+
+const struct inode_operations pipe_iops = {
+	.getattr	= pipe_getattr,
+};
+
 static int __init init_pipe_fs(void)
 {
 	int err = register_filesystem(&pipe_fs_type);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index eb86433..89103b9 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1973,6 +1973,7 @@ extern const struct file_operations def_blk_fops;
 extern const struct file_operations def_chr_fops;
 extern const struct file_operations bad_sock_fops;
 extern const struct file_operations def_fifo_fops;
+extern const struct inode_operations pipe_iops;
 #ifdef CONFIG_BLOCK
 extern int ioctl_by_bdev(struct block_device *, unsigned, unsigned long);
 extern int blkdev_ioctl(struct block_device *, fmode_t, unsigned, unsigned long);
--
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