Re: [f2fs-dev] [PATCH v2] f2fs: introduce F2FS_IOC_START_ATOMIC_REPLACE

From: Chao Yu
Date: Thu Sep 29 2022 - 18:55:05 EST

On 2022/9/30 0:13, Daeho Jeong wrote:
On Thu, Sep 29, 2022 at 12:36 AM Chao Yu <chao@xxxxxxxxxx> wrote:

On 2022/9/20 9:40, Daeho Jeong wrote:
From: Daeho Jeong <daehojeong@xxxxxxxxxx>

introduce a new ioctl to replace the whole content of a file atomically,
which means it induces truncate and content update at the same time.
We can start it with F2FS_IOC_START_ATOMIC_REPLACE and complete it with
F2FS_IOC_COMMIT_ATOMIC_WRITE. Or abort it with
F2FS_IOC_ABORT_ATOMIC_WRITE.

Signed-off-by: Daeho Jeong <daehojeong@xxxxxxxxxx>
---
v2: add undefined ioctl number reported by <lkp@xxxxxxxxx>
---
fs/f2fs/data.c | 3 +++
fs/f2fs/f2fs.h | 1 +
fs/f2fs/file.c | 12 ++++++++++--
fs/f2fs/segment.c | 14 +++++++++++++-
include/uapi/linux/f2fs.h | 1 +
5 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 6cd29a575105..d3d32db3a25d 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -3438,6 +3438,9 @@ static int prepare_atomic_write_begin(struct f2fs_sb_info *sbi,
else if (*blk_addr != NULL_ADDR)
return 0;

+ if (is_inode_flag_set(inode, FI_ATOMIC_REPLACE))
+ goto reserve_block;
+
/* Look for the block in the original inode */
err = __find_data_block(inode, index, &ori_blk_addr);
if (err)
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 539da7f12cfc..2c49da12d6d8 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -764,6 +764,7 @@ enum {
FI_COMPRESS_RELEASED, /* compressed blocks were released */
FI_ALIGNED_WRITE, /* enable aligned write */
FI_COW_FILE, /* indicate COW file */
+ FI_ATOMIC_REPLACE, /* indicate atomic replace */
FI_MAX, /* max flag, never be used */
};

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 4f9b80c41b1e..4abd9d2a55b3 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -1982,7 +1982,7 @@ static int f2fs_ioc_getversion(struct file *filp, unsigned long arg)
return put_user(inode->i_generation, (int __user *)arg);
}

-static int f2fs_ioc_start_atomic_write(struct file *filp)
+static int f2fs_ioc_start_atomic_write(struct file *filp, bool truncate)
{
struct inode *inode = file_inode(filp);
struct user_namespace *mnt_userns = file_mnt_user_ns(filp);
@@ -2051,6 +2051,12 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)

isize = i_size_read(inode);
fi->original_i_size = isize;
+ if (truncate) {
+ set_inode_flag(inode, FI_ATOMIC_REPLACE);
+ truncate_inode_pages_final(inode->i_mapping);
+ f2fs_i_size_write(inode, 0);
+ isize = 0;
+ }

Hi Daeho,

isize should be updated after tagging inode as atomic_write one?
otherwise f2fs_mark_inode_dirty_sync() may update isize to inode page,
latter checkpoint may persist that change? IIUC...

Thanks,

Hi Chao,

The first patch of this patchset prevents the inode page from being
updated as dirty for atomic file cases.
Is there any other chances for the inode page to be marked as dirty?

I mean:

Thread A Thread B
- f2fs_ioc_start_atomic_write
- f2fs_i_size_write(inode, 0)
- f2fs_mark_inode_dirty_sync
- checkpoint
- persist inode with incorrect zero isize

- set_inode_flag(inode, FI_ATOMIC_FILE)

Am I missing something?

Thanks,


Thanks,


f2fs_i_size_write(fi->cow_inode, isize);

spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
@@ -4080,7 +4086,9 @@ static long __f2fs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
case FS_IOC_GETVERSION:
return f2fs_ioc_getversion(filp, arg);
case F2FS_IOC_START_ATOMIC_WRITE:
- return f2fs_ioc_start_atomic_write(filp);
+ return f2fs_ioc_start_atomic_write(filp, false);
+ case F2FS_IOC_START_ATOMIC_REPLACE:
+ return f2fs_ioc_start_atomic_write(filp, true);
case F2FS_IOC_COMMIT_ATOMIC_WRITE:
return f2fs_ioc_commit_atomic_write(filp);
case F2FS_IOC_ABORT_ATOMIC_WRITE:
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 143b7ea0fb8e..c524538a9013 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -263,14 +263,26 @@ static void __complete_revoke_list(struct inode *inode, struct list_head *head,
bool revoke)
{
struct revoke_entry *cur, *tmp;
+ pgoff_t start_index = 0;
+ bool truncate = is_inode_flag_set(inode, FI_ATOMIC_REPLACE);

list_for_each_entry_safe(cur, tmp, head, list) {
- if (revoke)
+ if (revoke) {
__replace_atomic_write_block(inode, cur->index,
cur->old_addr, NULL, true);
+ } else if (truncate) {
+ f2fs_truncate_hole(inode, start_index, cur->index);
+ start_index = cur->index + 1;
+ }
+
list_del(&cur->list);
kmem_cache_free(revoke_entry_slab, cur);
}
+
+ if (!revoke && truncate) {
+ f2fs_do_truncate_blocks(inode, start_index * PAGE_SIZE, false);
+ clear_inode_flag(inode, FI_ATOMIC_REPLACE);
+ }
}

static int __f2fs_commit_atomic_write(struct inode *inode)
diff --git a/include/uapi/linux/f2fs.h b/include/uapi/linux/f2fs.h
index 3121d127d5aa..955d440be104 100644
--- a/include/uapi/linux/f2fs.h
+++ b/include/uapi/linux/f2fs.h
@@ -42,6 +42,7 @@
struct f2fs_comp_option)
#define F2FS_IOC_DECOMPRESS_FILE _IO(F2FS_IOCTL_MAGIC, 23)
#define F2FS_IOC_COMPRESS_FILE _IO(F2FS_IOCTL_MAGIC, 24)
+#define F2FS_IOC_START_ATOMIC_REPLACE _IO(F2FS_IOCTL_MAGIC, 25)

/*
* should be same as XFS_IOC_GOINGDOWN.