Re: [PATCH 3/8][e2fsprogs] add new -D <desc-size> option to mkfs

[Mingming Cao <cmm@us.ibm.com>]

On Thu, 2007-08-30 at 17:37 +0200, Valerie Clement wrote:
> From: Valerie Clement <valerie.clement@bull.net>
> 
> This patch adds a new option -D <descriptor-size> to mkfs to allow creating
> ext4 filesystems with larger group descriptor size.
> 
> By default, the group descriptor size is 32 bytes.
> To support 64-bit physical block numbers and thus to be able to use filesystems
>  > 16TB, the group descriptor size must be increased to 64 bytes.
> 

Could you explain a bit more why we need this option? It seems to me we
could make the block group descriptor size to 64bytes whenever creating
a ext4 filesystem by default. Is there any case we need to create ext4
with old 32 bytes block group descriptors?

> Use mkfs -t ext4 -D 64 to create an ext4 filesystem with 64-byte group
> descriptor size. This set the EXT4_FEATURE_INCOMPAT_64BIT flag on device.
> 
> The descriptor size is limited to a power-of-two value and to the block size.
> 
> Signed-off-by: Valerie Clement <valerie.clement@bull.net>
> ---
> 
>  lib/ext2fs/ext2_fs.h    |    7 +++++++
>  lib/ext2fs/initialize.c |    1 +
>  misc/mke2fs.c           |   33 +++++++++++++++++++++++++++++++--
>  3 files changed, 39 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/ext2fs/ext2_fs.h b/lib/ext2fs/ext2_fs.h
> index a316665..f6e8b36 100644
> --- a/lib/ext2fs/ext2_fs.h
> +++ b/lib/ext2fs/ext2_fs.h
> @@ -217,6 +217,13 @@ struct ext2_dx_countlimit {
>  /*
>   * Macro-instructions used to manage group descriptors
>   */
> +#define EXT2_MIN_DESC_SIZE		32
> +#define EXT2_MIN_DESC_SIZE_64BIT	64
> +#define EXT2_MAX_DESC_SIZE		EXT2_MIN_BLOCK_SIZE
> +#define EXT2_DESC_SIZE(s)						\
> +	((EXT2_SB(s)->s_feature_incompat & EXT4_FEATURE_INCOMPAT_64BIT) ? \
> +	 (s)->s_desc_size : EXT2_MIN_DESC_SIZE)
> +
>  #define EXT2_BLOCKS_PER_GROUP(s)	(EXT2_SB(s)->s_blocks_per_group)
>  #define EXT2_INODES_PER_GROUP(s)	(EXT2_SB(s)->s_inodes_per_group)
>  #define EXT2_INODES_PER_BLOCK(s)	(EXT2_BLOCK_SIZE(s)/EXT2_INODE_SIZE(s))
> diff --git a/lib/ext2fs/initialize.c b/lib/ext2fs/initialize.c
> index 16e9eaa..ee7af93 100644
> --- a/lib/ext2fs/initialize.c
> +++ b/lib/ext2fs/initialize.c
> @@ -149,6 +149,7 @@ errcode_t ext2fs_initialize(const char *name, int flags,
> 
>  	set_field(s_log_block_size, 0);	/* default blocksize: 1024 bytes */
>  	set_field(s_log_frag_size, 0); /* default fragsize: 1024 bytes */
> +	set_field(s_desc_size, 0);
>  	set_field(s_first_data_block, super->s_log_block_size ? 0 : 1);
>  	set_field(s_max_mnt_count, EXT2_DFL_MAX_MNT_COUNT);
>  	set_field(s_errors, EXT2_ERRORS_DEFAULT);
> diff --git a/misc/mke2fs.c b/misc/mke2fs.c
> index 4a6cace..115eef9 100644
> --- a/misc/mke2fs.c
> +++ b/misc/mke2fs.c
> @@ -96,7 +96,7 @@ static void usage(void)
>  {
>  	fprintf(stderr, _("Usage: %s [-c|-t|-l filename] [-b block-size] "
>  	"[-f fragment-size]\n\t[-i bytes-per-inode] [-I inode-size] "
> -	"[-j] [-J journal-options]\n"
> +	"[-D descriptor-size] [-j] [-J journal-options]\n"
>  	"\t[-N number-of-inodes] [-m reserved-blocks-percentage] "
>  	"[-o creator-os]\n\t[-g blocks-per-group] [-L volume-label] "
>  	"[-M last-mounted-directory]\n\t[-O feature[,...]] "
> @@ -911,6 +911,7 @@ static void PRS(int argc, char *argv[])
>  	int		blocksize = 0;
>  	int		inode_ratio = 0;
>  	int		inode_size = 0;
> +	int		desc_size = 0;
>  	double		reserved_ratio = 5.0;
>  	int		sector_size = 0;
>  	int		show_version_only = 0;
> @@ -993,7 +994,7 @@ static void PRS(int argc, char *argv[])
>  	}
> 
>  	while ((c = getopt (argc, argv,
> -		    "b:cf:g:i:jl:m:no:qr:s:tvE:FI:J:L:M:N:O:R:ST:V")) != EOF) {
> +		    "b:cf:g:i:jl:m:no:qr:s:tvD:E:FI:J:L:M:N:O:R:ST:V")) != EOF) {
>  		switch (c) {
>  		case 'b':
>  			blocksize = strtol(optarg, &tmp, 0);
> @@ -1110,6 +1111,14 @@ static void PRS(int argc, char *argv[])
>  				exit(1);
>  			}
>  			break;
> +		case 'D':
> +			desc_size = strtoul(optarg, &tmp, 0);
> +			if (*tmp) {
> +				com_err(program_name, 0,
> +					_("invalid descriptor size - %s"), optarg);
> +				exit(1);
> +			}
> +			break;
>  		case 'v':
>  			verbose = 1;
>  			break;
> @@ -1439,6 +1448,26 @@ static void PRS(int argc, char *argv[])
>  		}
>  	}
> 
> +	if (desc_size) {
> +		if (desc_size < EXT2_MIN_DESC_SIZE ||
> +		    desc_size > EXT2_BLOCK_SIZE(&fs_param) ||
> +		    desc_size & (desc_size -1)) {
> +			com_err(program_name, 0,
> +				_("invalid descriptor size %d (min %d/max %d)"),
> +				desc_size, EXT2_MIN_DESC_SIZE,
> +				blocksize);
> +			exit(1);
> +		}
> +		if (desc_size != EXT2_MIN_DESC_SIZE)
> +			fprintf(stderr, _("Warning: %d-byte descriptors not "
> +				"usable on older systems\n"),
> +				desc_size);
> +		fs_param.s_desc_size = desc_size;
> +		if (desc_size > EXT2_MIN_DESC_SIZE)
> +			fs_param.s_feature_incompat |= EXT4_FEATURE_INCOMPAT_64BIT;
> +	}
> +
> +
>  	if (!force && fs_param.s_blocks_count >= ((unsigned) 1 << 31)) {
>  		com_err(program_name, 0,
>  			_("Filesystem too large.  No more than 2**31-1 blocks\n"
> 
> 
> -
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