linux-ext4 - Re: [PATCH 1/1 linux-next] ext4: make online resizing conditional

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Date:   Thu, 20 Oct 2016 14:46:16 -0600
From:   Andreas Dilger <adilger@...ger.ca>
To:     Fabian Frederick <fabf@...net.be>
Cc:     tytso@....edu, Andreas Dilger <adilger.kernel@...ger.ca>,
        linux-kernel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 1/1 linux-next] ext4: make online resizing conditional

On Oct 20, 2016, at 12:37 PM, Fabian Frederick <fabf@...net.be> wrote:
> 
> This patch tries to address the following comment in ext4/resize.c
> "This could probably be made into a module, because it is not often in use."
> 
> Having ext4 resizing in a module would give a lot of depmod dependency cycles
> but we can make it an option.
> 
> resize.h has been added for more readability.
> 
> Tried the following resizing:
> dd if=/dev/zero of=ddext4 bs=1M count=100
> losetup -f ddext4
> mkfs -t ext4 /dev/loop0
> losetup -D
> dd if=/dev/zero of=ddappend bs=1M count=50
> cat ddappend >> ddext4
> losetup -f ddext4
> mount /dev/loop0 /mnt
> resize2fs /dev/loop0
> 
> With option disabled:
> "Operation not supported While checking for on-line resizing support"

Patch looks mostly good, some comments and cleanups below.

> Signed-off-by: Fabian Frederick <fabf@...net.be>
> ---
> fs/ext4/Kconfig  |  7 +++++++
> fs/ext4/Makefile |  3 ++-
> fs/ext4/ext4.h   | 12 ------------
> fs/ext4/ioctl.c  |  1 +
> fs/ext4/resize.c |  2 +-
> fs/ext4/resize.h | 42 ++++++++++++++++++++++++++++++++++++++++++
> 6 files changed, 53 insertions(+), 14 deletions(-)
> create mode 100644 fs/ext4/resize.h
> 
> diff --git a/fs/ext4/Kconfig b/fs/ext4/Kconfig
> index e38039f..2ec35c3 100644
> --- a/fs/ext4/Kconfig
> +++ b/fs/ext4/Kconfig
> @@ -122,3 +122,10 @@ config EXT4_DEBUG
> 	  If you select Y here, then you will be able to turn on debugging
> 	  with a command such as:
> 		echo 1 > /sys/module/ext4/parameters/mballoc_debug
> +
> +config EXT4_RESIZE
> +	bool "EXT4 resize"
> +	depends on EXT4_FS
> +	default y
> +	help
> +	  Support online ext4 partition resizing.
> diff --git a/fs/ext4/Makefile b/fs/ext4/Makefile
> index 354103f..efe6579 100644
> --- a/fs/ext4/Makefile
> +++ b/fs/ext4/Makefile
> @@ -5,10 +5,11 @@
> obj-$(CONFIG_EXT4_FS) += ext4.o
> 
> ext4-y	:= balloc.o bitmap.o dir.o file.o fsync.o ialloc.o inode.o page-io.o \
> -		ioctl.o namei.o super.o symlink.o hash.o resize.o extents.o \
> +		ioctl.o namei.o super.o symlink.o hash.o extents.o \
> 		ext4_jbd2.o migrate.o mballoc.o block_validity.o move_extent.o \
> 		mmp.o indirect.o extents_status.o xattr.o xattr_user.o \
> 		xattr_trusted.o inline.o readpage.o sysfs.o
> 
> ext4-$(CONFIG_EXT4_FS_POSIX_ACL)	+= acl.o
> ext4-$(CONFIG_EXT4_FS_SECURITY)		+= xattr_security.o
> +ext4-$(CONFIG_EXT4_RESIZE)		+= resize.o
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 282a51b..819a07b 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -2555,14 +2555,6 @@ extern int ext4_generic_delete_entry(handle_t *handle,
> 				     int csum_size);
> extern bool ext4_empty_dir(struct inode *inode);
> 
> -/* resize.c */
> -extern int ext4_group_add(struct super_block *sb,
> -				struct ext4_new_group_data *input);
> -extern int ext4_group_extend(struct super_block *sb,
> -				struct ext4_super_block *es,
> -				ext4_fsblk_t n_blocks_count);
> -extern int ext4_resize_fs(struct super_block *sb, ext4_fsblk_t n_blocks_count);
> -
> /* super.c */
> extern int ext4_seq_options_show(struct seq_file *seq, void *offset);
> extern int ext4_calculate_overhead(struct super_block *sb);
> @@ -3239,10 +3231,6 @@ static inline void ext4_inode_resume_unlocked_dio(struct inode *inode)
> 					    EXT4_WQ_HASH_SZ])
> extern wait_queue_head_t ext4__ioend_wq[EXT4_WQ_HASH_SZ];
> 
> -#define EXT4_RESIZING	0
> -extern int ext4_resize_begin(struct super_block *sb);
> -extern void ext4_resize_end(struct super_block *sb);
> -
> static inline void ext4_set_io_unwritten_flag(struct inode *inode,
> 					      struct ext4_io_end *io_end)
> {
> diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
> index bf5ae8e..81d28d2 100644
> --- a/fs/ext4/ioctl.c
> +++ b/fs/ext4/ioctl.c
> @@ -18,6 +18,7 @@
> #include <asm/uaccess.h>
> #include "ext4_jbd2.h"
> #include "ext4.h"
> +#include "resize.h"
> 
> /**
>  * Swap memory between @a and @b for @len bytes.
> diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
> index cf68100..8192194 100644
> --- a/fs/ext4/resize.c
> +++ b/fs/ext4/resize.c
> @@ -5,7 +5,6 @@
>  *
>  * Copyright (C) 2001, 2002 Andreas Dilger <adilger@...sterfs.com>
>  *
> - * This could probably be made into a module, because it is not often in use.

This comment is probably still valid?

>  */
> 
> 
> @@ -15,6 +14,7 @@
> #include <linux/slab.h>
> 
> #include "ext4_jbd2.h"
> +#include "resize.h"
> 
> int ext4_resize_begin(struct super_block *sb)
> {
> diff --git a/fs/ext4/resize.h b/fs/ext4/resize.h
> new file mode 100644
> index 0000000..1375434
> --- /dev/null
> +++ b/fs/ext4/resize.h
> @@ -0,0 +1,42 @@
> +/*
> + * linux/fs/ext4/resize.h
> + *
> + */
> +
> +#define EXT4_RESIZING	0

Moving this here is a bit confusing, since it has no context of what it is
used for.  This only makes sense together with ext4_resize_{begin,end}(),
so it should be declared below, inside CONFIG_EXT4_RESIZE.

It also wouldn't hurt to rename this something like EXT4_RESIZE_ACTIVE,
and add to the comment at s_resize_flags indicating it is using
EXT4_RESIZE_* bits.

> +
> +#if IS_ENABLED(CONFIG_EXT4_RESIZE)

IS_ENABLED() seems unnecessary, as most CONFIG_* symbols are checked via

#ifdef CONFIG_EXT4_RESIZE

Is there some reason to use IS_ENABLED() for this?  My quick reading of
the ugly macro series this uses is for CONFIG_ values that may be 0 or 1,
and #ifdef CONFIG_* is fine for values that may be "y" or "m".

> +extern int ext4_resize_fs(struct super_block *, ext4_fsblk_t);
> +extern int ext4_resize_begin(struct super_block *);
> +extern void ext4_resize_end(struct super_block *);
> +extern int ext4_group_add(struct super_block *, struct ext4_new_group_data *);
> +extern int ext4_group_extend(struct super_block *, struct ext4_super_block *,
> +			     ext4_fsblk_t);
> +#else
> +static int ext4_resize_begin(struct super_block *sb)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
> +static void ext4_resize_end(struct super_block *sb)
> +{
> +}
> +
> +static inline int ext4_group_add(struct super_block *sb,
> +				 struct ext4_new_group_data *input)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
> +static inline int ext4_group_extend(struct super_block *sb,
> +		struct ext4_super_block *es, ext4_fsblk_t n_blocks_count)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
> +static inline int ext4_resize_fs(struct super_block *sb,
> +				 ext4_fsblk_t n_blocks_count)
> +{
> +	return -EOPNOTSUPP;
> +}
> +#endif
> --
> 2.9.3
> 


Cheers, Andreas






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