Hi Chris,
These ioctls let a user application hold a transaction open while it
performs a series of operations. A final ioctl does a sync on the fs
(closing the current transaction). This is the main requirement for
Ceph's OSD to be able to keep the data it's storing in a btrfs volume
consistent, and AFAICS it works just fine. The application would do
something like
fd = ::open("some/file", O_RDONLY);
::ioctl(fd, BTRFS_IOC_TRANS_START);
/* do a bunch of stuff */
::ioctl(fd, BTRFS_IOC_TRANS_END);
or just
::close(fd);
And to ensure it commits to disk,
::ioctl(fd, BTRFS_IOC_SYNC);
When a transaction is held open, the trans_handle is attached to the
struct file (via private_data) so that it will get cleaned up if the
process dies unexpectedly. A held transaction is also ended on fsync() to
avoid a deadlock. There may be other places I missed?
A misbehaving application could also deliberately hold a transaction open,
effectively locking up the FS, so it may make sense to restrict something
like this to root or something.
Anyway, does this look reasonable?
Thanks-
sage
diff -r e4cd88595ed7 ctree.h
--- a/ctree.h Thu Feb 21 14:54:12 2008 -0500
+++ b/ctree.h Tue Apr 22 12:08:53 2008 -0700
@@ -1179,6 +1179,7 @@ void btrfs_destroy_inode(struct inode *i
void btrfs_destroy_inode(struct inode *inode);
int btrfs_init_cachep(void);
void btrfs_destroy_cachep(void);
+long btrfs_ioctl_trans_end(struct file *file);
long btrfs_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
struct inode *btrfs_iget_locked(struct super_block *s, u64 objectid,
struct btrfs_root *root);
@@ -1199,6 +1200,8 @@ int btrfs_drop_extents(struct btrfs_tran
int btrfs_drop_extents(struct btrfs_trans_handle *trans,
struct btrfs_root *root, struct inode *inode,
u64 start, u64 end, u64 inline_limit, u64 *hint_block);
+int btrfs_file_release(struct inode *inode, struct file *file);
+
/* tree-defrag.c */
int btrfs_defrag_leaves(struct btrfs_trans_handle *trans,
struct btrfs_root *root, int cache_only);
@@ -1217,4 +1220,5 @@ int btrfs_delete_xattrs(struct btrfs_tra
struct btrfs_root *root, struct inode *inode);
/* super.c */
u64 btrfs_parse_size(char *str);
+int btrfs_sync_fs(struct super_block *sb, int wait);
#endif
diff -r e4cd88595ed7 file.c
--- a/file.c Thu Feb 21 14:54:12 2008 -0500
+++ b/file.c Tue Apr 22 12:08:53 2008 -0700
@@ -941,6 +941,8 @@ static int btrfs_sync_file(struct file *
/*
* ok we haven't committed the transaction yet, lets do a commit
*/
+ if (file->private_data)
+ btrfs_ioctl_trans_end(file);
trans = btrfs_start_transaction(root, 1);
if (!trans) {
ret = -ENOMEM;
@@ -950,6 +952,13 @@ out:
out:
mutex_unlock(&root->fs_info->fs_mutex);
return ret > 0 ? EIO : ret;
+}
+
+int btrfs_file_release(struct inode *inode, struct file *file)
+{
+ if (file->private_data)
+ btrfs_ioctl_trans_end(file);
+ return 0;
}
static struct vm_operations_struct btrfs_file_vm_ops = {
@@ -980,6 +989,7 @@ struct file_operations btrfs_file_operat
.write = btrfs_file_write,
.mmap = btrfs_file_mmap,
.open = generic_file_open,
+ .release = btrfs_file_release,
.fsync = btrfs_sync_file,
.unlocked_ioctl = btrfs_ioctl,
#ifdef CONFIG_COMPAT
diff -r e4cd88595ed7 inode.c
--- a/inode.c Thu Feb 21 14:54:12 2008 -0500
+++ b/inode.c Tue Apr 22 12:08:53 2008 -0700
@@ -2690,6 +2690,42 @@ static int btrfs_ioctl_defrag(struct fil
return 0;
}
+long btrfs_ioctl_trans_start(struct file *file)
+{
+ struct inode *inode = fdentry(file)->d_inode;
+ struct btrfs_root *root = BTRFS_I(inode)->root;
+ struct btrfs_trans_handle *trans;
+ int ret = 0;
+
+ if (file->private_data)
+ return -EINPROGRESS;
+ mutex_lock(&root->fs_info->fs_mutex);
+ trans = btrfs_start_transaction(root, 0);
+ if (trans)
+ file->private_data = trans;
+ else
+ ret = -ENOMEM;
+ /*printk(KERN_INFO "btrfs_ioctl_trans_start on %p\n", file);*/
+ mutex_unlock(&root->fs_info->fs_mutex);
+ return ret;
+}
+
+long btrfs_ioctl_trans_end(struct file *file)
+{
+ struct inode *inode = fdentry(file)->d_inode;
+ struct btrfs_root *root = BTRFS_I(inode)->root;
+ struct btrfs_trans_handle *trans = file->private_data;
+
+ if (!trans)
+ return -EINVAL;
+ /*printk(KERN_INFO "btrfs_ioctl_trans_end on %p\n", file);*/
+ mutex_lock(&root->fs_info->fs_mutex);
+ btrfs_end_transaction(trans, root);
+ file->private_data = 0;
+ mutex_unlock(&root->fs_info->fs_mutex);
+ return 0;
+}
+
long btrfs_ioctl(struct file *file, unsigned int
cmd, unsigned long arg)
{
@@ -2702,6 +2738,13 @@ long btrfs_ioctl(struct file *file, unsi
return btrfs_ioctl_defrag(file);
case BTRFS_IOC_RESIZE:
return btrfs_ioctl_resize(root, (void __user *)arg);
+ case BTRFS_IOC_TRANS_START:
+ return btrfs_ioctl_trans_start(file);
+ case BTRFS_IOC_TRANS_END:
+ return btrfs_ioctl_trans_end(file);
+ case BTRFS_IOC_SYNC:
+ btrfs_sync_fs(file->f_dentry->d_sb, 1);
+ return 0;
}
return -ENOTTY;
@@ -3019,6 +3062,7 @@ static struct file_operations btrfs_dir_
#ifdef CONFIG_COMPAT
.compat_ioctl = btrfs_ioctl,
#endif
+ .release = btrfs_file_release,
};
static struct extent_io_ops btrfs_extent_io_ops = {
diff -r e4cd88595ed7 ioctl.h
--- a/ioctl.h Thu Feb 21 14:54:12 2008 -0500
+++ b/ioctl.h Tue Apr 22 12:08:53 2008 -0700
@@ -32,4 +32,9 @@ struct btrfs_ioctl_vol_args {
struct btrfs_ioctl_vol_args)
#define BTRFS_IOC_RESIZE _IOW(BTRFS_IOCTL_MAGIC, 3, \
struct btrfs_ioctl_vol_args)
+
+#define BTRFS_IOC_TRANS_START _IO(BTRFS_IOCTL_MAGIC, 6)
+#define BTRFS_IOC_TRANS_END _IO(BTRFS_IOCTL_MAGIC, 7)
+#define BTRFS_IOC_SYNC _IO(BTRFS_IOCTL_MAGIC, 8)
#endif
+
diff -r e4cd88595ed7 super.c
--- a/super.c Thu Feb 21 14:54:12 2008 -0500
+++ b/super.c Tue Apr 22 12:08:53 2008 -0700
@@ -284,7 +284,7 @@ fail_close:
return err;
}
-static int btrfs_sync_fs(struct super_block *sb, int wait)
+int btrfs_sync_fs(struct super_block *sb, int wait)
{
struct btrfs_trans_handle *trans;
struct btrfs_root *root;
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