[RFC][PATCH 4/8] file c/r: expose functions to query fs support

[Dave Hansen <dave@linux.vnet.ibm.com>]

This pair of functions will check to see whether a given
'struct file' can be checkpointed.  If it can't be, the
"explain" function can also give a description why.

Signed-off-by: Dave Hansen <dave@linux.vnet.ibm.com>
---

 linux-2.6.git-dave/checkpoint/ckpt_file.c     |   46 ++++++++++++++++++++++++++
 linux-2.6.git-dave/include/linux/checkpoint.h |   18 ++++++++++
 2 files changed, 64 insertions(+)

diff -puN checkpoint/ckpt_file.c~cr-explain-unckpt-file checkpoint/ckpt_file.c
--- linux-2.6.git/checkpoint/ckpt_file.c~cr-explain-unckpt-file	2009-02-27 12:07:38.000000000 -0800
+++ linux-2.6.git-dave/checkpoint/ckpt_file.c	2009-02-27 12:07:38.000000000 -0800
@@ -72,6 +72,52 @@ int cr_scan_fds(struct files_struct *fil
 	return n;
 }
 
+int fs_is_cr_able(struct file_system_type *fs_type)
+{
+	if (fs_type->fs_flags & FS_CHECKPOINTABLE)
+		return 1;
+	/*
+	 * We assume that all block-based filesystems that
+	 * need devices work.  This covers all of the
+	 * "important" fs's by default like ext*.  If this
+	 * assumption becomes untrue, we may need a
+	 * NOT_CHECKPOINTABLE flag in the future
+	 */
+	if (fs_type->fs_flags & FS_REQUIRES_DEV)
+		return 1;
+	return 0;
+}
+
+int cr_explain_file(struct file *file, char *explain, int left)
+{
+	struct inode *inode = file->f_dentry->d_inode;
+	struct file_system_type *fs_type = inode->i_sb->s_type;
+
+	if (!fs_is_cr_able(fs_type))
+		return snprintf(explain, left,
+				" (%s does not support checkpoint)",
+				fs_type->name);
+
+	if (special_file(inode->i_mode))
+		return snprintf(explain, left, " (special file)");
+
+	return 0;
+}
+
+int cr_file_supported(struct file *file)
+{
+	struct inode *inode = file->f_dentry->d_inode;
+	struct file_system_type *fs_type = inode->i_sb->s_type;
+
+	if (fs_is_cr_able(fs_type))
+		return 0;
+
+	if (special_file(inode->i_mode))
+		return 0;
+
+	return 1;
+}
+
 /* cr_write_fd_data - dump the state of a given file pointer */
 static int cr_write_fd_data(struct cr_ctx *ctx, struct file *file, int parent)
 {
diff -puN include/linux/checkpoint.h~cr-explain-unckpt-file include/linux/checkpoint.h
--- linux-2.6.git/include/linux/checkpoint.h~cr-explain-unckpt-file	2009-02-27 12:07:38.000000000 -0800
+++ linux-2.6.git-dave/include/linux/checkpoint.h	2009-02-27 12:07:38.000000000 -0800
@@ -13,6 +13,8 @@
 #include <linux/path.h>
 #include <linux/fs.h>
 
+#ifdef CONFIG_CHECKPOINT_RESTART
+
 #define CR_VERSION  2
 
 struct cr_ctx {
@@ -99,4 +101,20 @@ extern int cr_read_files(struct cr_ctx *
 
 #define pr_fmt(fmt) "[%d:c/r:%s] " fmt, task_pid_vnr(current), __func__
 
+int cr_explain_file(struct file *file, char *explain, int left);
+int cr_file_supported(struct file *file);
+
+#else /* !CONFIG_CHECKPOINT_RESTART */
+
+static inline int cr_explain_file(struct file *file, char *explain, int left)
+{
+	return 0;
+}
+
+int cr_file_supported(struct file *file)
+{
+	return 0;
+}
+
+#endif /* CONFIG_CHECKPOINT_RESTART */
 #endif /* _CHECKPOINT_CKPT_H_ */
_