On Sun, Jun 24, 2012 at 11:42:55PM -0700, Fredrick wrote:
> Hello Ext4 developers,
>
> When calling fallocate on ext4 fs, ext4_fallocate does not initialize
> the extents. The extents are allocated only when they are actually
> written. This is causing a problem for us. Our programs create many
> "write only once" files as large as 1G on ext4 very rapidly at times.
> We thought fallocate would solve the problem. But it didnt.
> If I change the EXT4_GET_BLOCKS_CREATE_UNINIT_EXT to
> just EXT4_GET_BLOCKS_CREATE in the ext4_map_blocks in the
> ext4_fallocate call,
> the extents get created in fallocate call itself. This is helping us.
> Now the write throughtput to the disk was close to 98%. When extents
> were not
> initialized, our disk throughput were only 70%.
>
> Can this change be made to ext4_fallocate?
Hi Fredrick,
I think that this patch maybe can help you. :-)
Actually I want to send a url for you from linux mailing list archive but
I cannot find it. After applying this patch, you can call ioctl(2) to
enable expose_stale_data flag, and then when you call fallocate(2), ext4
create initialized extents for you. This patch cannot be merged into
upstream kernel because it brings a huge security hole.
Regards,
Zheng
From: Zheng Liu <wenqing.lz@xxxxxxxxxx>
Date: Wed, 6 Jun 2012 11:10:57 +0800
Subject: [RFC][PATCH v2] ext4: add expose_stale_data flag in fallocate
Here is the v2 of FALLOC_FL_NO_HIDE_STALE in fallocate. Now no new flag is
added into vfs in order to reduce the impacts and avoid a huge security hole.
The application cannot call fallocate with a new flag to create an unwritten
extent. It needs to call ioctl to enable/disable this feature. Meanwhile, in
ioctl, filesystem will check CAP_SYS_RAWIO to ensure that the user has a
privilege to switch on/off it. Currently, I only implement it in ext4.
Even though I try to reduce its impact, this feature still brings a security
hole. So the application must ensure that it initializes an unwritten extent
by itself before reading it, and it is used in a limited environment.
v1 -> v2:
* remove FALLOC_FL_NO_HIDE_STALE flag in vfs
* add 'i_expose_stale_data' in ext4 to enable/disable it
Signed-off-by: Zheng Liu <wenqing.lz@xxxxxxxxxx>
---
fs/ext4/ext4.h | 5 +++++
fs/ext4/extents.c | 6 +++++-
fs/ext4/ioctl.c | 43 +++++++++++++++++++++++++++++++++++++++++++
fs/ext4/super.c | 1 +
4 files changed, 54 insertions(+), 1 deletions(-)
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index cfc4e01..61da070 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -606,6 +606,8 @@ enum {
#define EXT4_IOC_ALLOC_DA_BLKS _IO('f', 12)
#define EXT4_IOC_MOVE_EXT _IOWR('f', 15, struct move_extent)
#define EXT4_IOC_RESIZE_FS _IOW('f', 16, __u64)
+#define EXT4_IOC_GET_EXPOSE_STALE _IOR('f', 17, int)
+#define EXT4_IOC_SET_EXPOSE_STALE _IOW('f', 18, int)
#if defined(__KERNEL__) && defined(CONFIG_COMPAT)
/*
@@ -925,6 +927,9 @@ struct ext4_inode_info {
/* Precomputed uuid+inum+igen checksum for seeding inode checksums */
__u32 i_csum_seed;
+
+ /* expose stale data in creating a new extent */
+ int i_expose_stale_data;
};
/*
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 91341ec..9ef883c 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4336,6 +4336,7 @@ static void ext4_falloc_update_inode(struct inode *inode,
long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
{
struct inode *inode = file->f_path.dentry->d_inode;
+ struct ext4_inode_info *ei = EXT4_I(inode);
handle_t *handle;
loff_t new_size;
unsigned int max_blocks;
@@ -4379,7 +4380,10 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
trace_ext4_fallocate_exit(inode, offset, max_blocks, ret);
return ret;
}
- flags = EXT4_GET_BLOCKS_CREATE_UNINIT_EXT;
+ if (ei->i_expose_stale_data)
+ flags = EXT4_GET_BLOCKS_CREATE;
+ else
+ flags = EXT4_GET_BLOCKS_CREATE_UNINIT_EXT;
if (mode & FALLOC_FL_KEEP_SIZE)
flags |= EXT4_GET_BLOCKS_KEEP_SIZE;
/*
diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index 8ad112a..fffb3eb 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -445,6 +445,47 @@ resizefs_out:
return 0;
}
+ case EXT4_IOC_GET_EXPOSE_STALE: {
+ int enable;
+
+ /* security check */
+ if (!capable(CAP_SYS_RAWIO))
+ return -EPERM;
+
+ /*
+ * currently only extent-based files support (pre)allocate with
+ * EXPOSE_STALE_DATA flag
+ */
+ if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)))
+ return -EOPNOTSUPP;
+
+ enable = ei->i_expose_stale_data;
+
+ return put_user(enable, (int __user *) arg);
+ }
+
+ case EXT4_IOC_SET_EXPOSE_STALE: {
+ int enable;
+
+ /* security check */
+ if (!capable(CAP_SYS_RAWIO))
+ return -EPERM;
+
+ /*
+ * currently only extent-based files support (pre)allocate with
+ * EXPOSE_STALE_DATA flag
+ */
+ if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)))
+ return -EOPNOTSUPP;
+
+ if (get_user(enable, (int __user *) arg))
+ return -EFAULT;
+
+ ei->i_expose_stale_data = enable;
+
+ return 0;
+ }
+
default:
return -ENOTTY;
}
@@ -508,6 +549,8 @@ long ext4_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
case EXT4_IOC_MOVE_EXT:
case FITRIM:
case EXT4_IOC_RESIZE_FS:
+ case EXT4_IOC_GET_EXPOSE_STALE:
+ case EXT4_IOC_SET_EXPOSE_STALE:
break;
default:
return -ENOIOCTLCMD;
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index eb7aa3e..3654bb8 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -988,6 +988,7 @@ static struct inode *ext4_alloc_inode(struct super_block *sb)
ei->i_datasync_tid = 0;
atomic_set(&ei->i_ioend_count, 0);
atomic_set(&ei->i_aiodio_unwritten, 0);
+ ei->i_expose_stale_data = 0;
return &ei->vfs_inode;
}
--
1.7.4.1
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