[Devel] [PATCH vz7] fuse: trust server file size unless opened

[Konstantin Khorenko]

Dima, please review the patch.

--
Best regards,

Konstantin Khorenko,
Virtuozzo Linux Kernel Team

On 12/15/2016 03:46 AM, Maxim Patlasov wrote:
> Before the patch, the only way to pick up updated file size from server (in a
> scenario when local inode was created earlier, then the file was updated
> from another node) was in fuse_open_common():
>
>> 		atomic_inc(&fi->num_openers);
>>
>> 		if (atomic_read(&fi->num_openers) == 1) {
>> 			err = fuse_getattr_size(inode, file, &size);
>> 			...
>> 			spin_lock(&fc->lock);
>> 			i_size_write(inode, size);
>> 			spin_unlock(&fc->lock);
>> 		}
>
> This is correct, but someone may ask about i_size w/o open, e.g.: ls -l foo.
> The patch ensures that every time the server reports us some file size, if no
> open-s happened yet (num_openers=0), fuse stores that server size in local
> inode->i_size. This resolves the following problem:
>
> # pstorage-mount -c test -l /var/log/f1.log /pcs1
> # pstorage-mount -c test -l /var/log/f2.log /pcs2
>
> # date > /pcs1/foo; ls -l /pcs1/foo /pcs2/foo
> -rwx------ 1 root root 29 Dec 14 16:31 /pcs1/foo
> -rwx------ 1 root root 29 Dec 14 16:31 /pcs2/foo
>
> # date >> /pcs1/foo; ls -l /pcs1/foo /pcs2/foo
> -rwx------ 1 root root 58 Dec 14 16:31 /pcs1/foo
> -rwx------ 1 root root 29 Dec 14 16:31 /pcs2/foo
>
> https://jira.sw.ru/browse/PSBM-57047
>
> Signed-off-by: Maxim Patlasov <mpatlasov at virtuozzo.com>
> ---
>  fs/fuse/file.c   |   12 +++++++++++-
>  fs/fuse/fuse_i.h |    3 +++
>  fs/fuse/inode.c  |    4 +++-
>  3 files changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index 9cad8c5..62967d2 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -296,12 +296,20 @@ int fuse_open_common(struct inode *inode, struct file *file, bool isdir)
>  		u64 size;
>
>  		mutex_lock(&inode->i_mutex);
> +
> +		spin_lock(&fc->lock);
>  		atomic_inc(&fi->num_openers);
>
>  		if (atomic_read(&fi->num_openers) == 1) {
> +			fi->i_size_unstable = 1;
> +			spin_unlock(&fc->lock);
>  			err = fuse_getattr_size(inode, file, &size);
>  			if (err) {
> +				spin_lock(&fc->lock);
>  				atomic_dec(&fi->num_openers);
> +				fi->i_size_unstable = 0;
> +				spin_unlock(&fc->lock);
> +
>  				mutex_unlock(&inode->i_mutex);
>  				fuse_release_common(file, FUSE_RELEASE);
>  				return err;
> @@ -309,8 +317,10 @@ int fuse_open_common(struct inode *inode, struct file *file, bool isdir)
>
>  			spin_lock(&fc->lock);
>  			i_size_write(inode, size);
> +			fi->i_size_unstable = 0;
> +			spin_unlock(&fc->lock);
> +		} else
>  			spin_unlock(&fc->lock);
> -		}
>
>  		mutex_unlock(&inode->i_mutex);
>  	}
> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
> index 1d24bf6..22eb9c9 100644
> --- a/fs/fuse/fuse_i.h
> +++ b/fs/fuse/fuse_i.h
> @@ -124,6 +124,9 @@ struct fuse_inode {
>
>  	/** Mostly to detect very first open */
>  	atomic_t num_openers;
> +
> +	/** Even though num_openers>0, trust server i_size */
> +	int i_size_unstable;
>  };
>
>  /** FUSE inode state bits */
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index 5ccecae..f606deb 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -97,6 +97,7 @@ static struct inode *fuse_alloc_inode(struct super_block *sb)
>  	fi->writectr = 0;
>  	fi->orig_ino = 0;
>  	fi->state = 0;
> +	fi->i_size_unstable = 0;
>  	INIT_LIST_HEAD(&fi->write_files);
>  	INIT_LIST_HEAD(&fi->rw_files);
>  	INIT_LIST_HEAD(&fi->queued_writes);
> @@ -226,7 +227,8 @@ void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
>  	 * extend local i_size without keeping userspace server in sync. So,
>  	 * attr->size coming from server can be stale. We cannot trust it.
>  	 */
> -	if (!is_wb || !S_ISREG(inode->i_mode))
> +	if (!is_wb || !S_ISREG(inode->i_mode) ||
> +	    !atomic_read(&fi->num_openers) || fi->i_size_unstable)
>  		i_size_write(inode, attr->size);
>  	spin_unlock(&fc->lock);
>
>
> .
>