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Subject[RFC][PATCH 8/9] vfs: Implement generic revoked file operations

revoked_file_ops is a set of file operations designed to be used
when a files backing store has been removed.

revoked_file_ops return 0 from reads (aka EOF). Tell poll the file is
always ready for I/O and return -EIO from all other operations.

This is designed to allow userspace to gracefully file descriptors
that enter this unusable state.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
---
fs/Makefile | 2 +-
fs/revoked_file.c | 181 ++++++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/fs.h | 2 +
3 files changed, 184 insertions(+), 1 deletions(-)
create mode 100644 fs/revoked_file.c
diff --git a/fs/Makefile b/fs/Makefile
index af6d047..7787ddd 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -11,7 +11,7 @@ obj-y := open.o read_write.o file_table.o super.o \
attr.o bad_inode.o file.o filesystems.o namespace.o \
seq_file.o xattr.o libfs.o fs-writeback.o \
pnode.o drop_caches.o splice.o sync.o utimes.o \
- stack.o fs_struct.o
+ stack.o fs_struct.o revoked_file.o

ifeq ($(CONFIG_BLOCK),y)
obj-y += buffer.o bio.o block_dev.o direct-io.o mpage.o ioprio.o
diff --git a/fs/revoked_file.c b/fs/revoked_file.c
new file mode 100644
index 0000000..9936693
--- /dev/null
+++ b/fs/revoked_file.c
@@ -0,0 +1,181 @@
+/*
+ * linux/fs/revoked_file.c
+ *
+ * Copyright (C) 1997, Stephen Tweedie
+ *
+ * Provide stub functions for unreadable inodes
+ *
+ * Fabian Frederick : August 2003 - All file operations assigned to EIO
+ *
+ * Eric Biederman : 8 April 2008 - Derivied from bad_inode.c
+ */
+
+#include <linux/fs.h>
+#include <linux/module.h>
+#include <linux/stat.h>
+#include <linux/time.h>
+#include <linux/namei.h>
+#include <linux/poll.h>
+
+static loff_t revoked_file_llseek(struct file *file, loff_t offset, int origin)
+{
+ return -EIO;
+}
+
+static ssize_t revoked_file_read(struct file *filp, char __user *buf,
+ size_t size, loff_t *ppos)
+{
+ return 0;
+}
+
+static ssize_t revoked_file_write(struct file *filp, const char __user *buf,
+ size_t siz, loff_t *ppos)
+{
+ return -EIO;
+}
+
+static ssize_t revoked_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
+ unsigned long nr_segs, loff_t pos)
+{
+ return 0;
+}
+
+static ssize_t revoked_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
+ unsigned long nr_segs, loff_t pos)
+{
+ return -EIO;
+}
+
+static int revoked_file_readdir(struct file *filp, void *dirent, filldir_t filldir)
+{
+ return -EIO;
+}
+
+static unsigned int revoked_file_poll(struct file *filp, poll_table *wait)
+{
+ return POLLIN | POLLOUT | POLLERR | POLLRDNORM | POLLWRNORM;
+}
+
+static int revoked_file_ioctl (struct inode *inode, struct file *filp,
+ unsigned int cmd, unsigned long arg)
+{
+ return -EIO;
+}
+
+static long revoked_file_unlocked_ioctl(struct file *file, unsigned cmd,
+ unsigned long arg)
+{
+ return -EIO;
+}
+
+static long revoked_file_compat_ioctl(struct file *file, unsigned int cmd,
+ unsigned long arg)
+{
+ return -EIO;
+}
+
+static int revoked_file_mmap(struct file *file, struct vm_area_struct *vma)
+{
+ return -EIO;
+}
+
+static int revoked_file_open(struct inode *inode, struct file *filp)
+{
+ return -EIO;
+}
+
+static int revoked_file_flush(struct file *file, fl_owner_t id)
+{
+ return 0;
+}
+
+static int revoked_file_release(struct inode *inode, struct file *filp)
+{
+ return 0;
+}
+
+static int revoked_file_fsync(struct file *file, struct dentry *dentry,
+ int datasync)
+{
+ return -EIO;
+}
+
+static int revoked_file_aio_fsync(struct kiocb *iocb, int datasync)
+{
+ return -EIO;
+}
+
+static int revoked_file_fasync(int fd, struct file *filp, int on)
+{
+ return -EIO;
+}
+
+static int revoked_file_lock(struct file *file, int cmd, struct file_lock *fl)
+{
+ return -EIO;
+}
+
+static ssize_t revoked_file_sendpage(struct file *file, struct page *page,
+ int off, size_t len, loff_t *pos, int more)
+{
+ return -EIO;
+}
+
+static unsigned long revoked_file_get_unmapped_area(struct file *file,
+ unsigned long addr, unsigned long len,
+ unsigned long pgoff, unsigned long flags)
+{
+ return -EIO;
+}
+
+static int revoked_file_check_flags(int flags)
+{
+ return -EIO;
+}
+
+static int revoked_file_flock(struct file *filp, int cmd, struct file_lock *fl)
+{
+ return -EIO;
+}
+
+static ssize_t revoked_file_splice_write(struct pipe_inode_info *pipe,
+ struct file *out, loff_t *ppos, size_t len,
+ unsigned int flags)
+{
+ return -EIO;
+}
+
+static ssize_t revoked_file_splice_read(struct file *in, loff_t *ppos,
+ struct pipe_inode_info *pipe, size_t len,
+ unsigned int flags)
+{
+ return -EIO;
+}
+
+const struct file_operations revoked_file_ops =
+{
+ .llseek = revoked_file_llseek,
+ .read = revoked_file_read,
+ .write = revoked_file_write,
+ .aio_read = revoked_file_aio_read,
+ .aio_write = revoked_file_aio_write,
+ .readdir = revoked_file_readdir,
+ .poll = revoked_file_poll,
+ .ioctl = revoked_file_ioctl,
+ .unlocked_ioctl = revoked_file_unlocked_ioctl,
+ .compat_ioctl = revoked_file_compat_ioctl,
+ .mmap = revoked_file_mmap,
+ .open = revoked_file_open,
+ .flush = revoked_file_flush,
+ .release = revoked_file_release,
+ .fsync = revoked_file_fsync,
+ .aio_fsync = revoked_file_aio_fsync,
+ .fasync = revoked_file_fasync,
+ .lock = revoked_file_lock,
+ .sendpage = revoked_file_sendpage,
+ .get_unmapped_area = revoked_file_get_unmapped_area,
+ .check_flags = revoked_file_check_flags,
+ .flock = revoked_file_flock,
+ .splice_write = revoked_file_splice_write,
+ .splice_read = revoked_file_splice_read,
+};
diff --git a/include/linux/fs.h b/include/linux/fs.h
index a82a2ea..2fb0871 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -896,6 +896,8 @@ extern int fops_substitute(struct file *file, const struct file_operations *f_op
extern void inode_fops_substitute(struct inode *inode,
const struct file_operations *f_op, struct vm_operations_struct *vm_ops);

+extern const struct file_operations revoked_file_ops;
+
extern struct mutex files_lock;
#define file_list_lock() mutex_lock(&files_lock);
#define file_list_unlock() mutex_unlock(&files_lock);
--
1.6.1.2.350.g88cc


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