Re: [RFC][PATCH 1/11][take 2] add new mkfs option to create ext4 filesystems

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

Valerie Clement wrote:
> This patch adds a new option '-D' to mkfs to allow creating ext4 
> filesystem.
> 
>  lib/ext2fs/ext2_fs.h    |    7 +++++++
>  lib/ext2fs/initialize.c |    1 +
>  misc/mke2fs.c           |   18 ++++++++++++++++--
>  3 files changed, 24 insertions(+), 2 deletions(-)
> 
> 
> 
> 
> 
> ------------------------------------------------------------------------
> 
> Index: e2fsprogs-1.39-tyt3-v7/misc/mke2fs.c
> ===================================================================
> --- e2fsprogs-1.39-tyt3-v7.orig/misc/mke2fs.c	2007-04-30 07:10:05.000000000 +0200
> +++ e2fsprogs-1.39-tyt3-v7/misc/mke2fs.c	2007-06-14 12:03:48.000000000 +0200
> @@ -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[,...]] "
> @@ -899,6 +899,7 @@ 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;
> @@ -977,7 +978,7 @@ 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);
> @@ -1094,6 +1095,14 @@ 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;
> @@ -1422,6 +1431,11 @@ static void PRS(int argc, char *argv[])
>  		}
>  	}
> 
> +	if (desc_size >= EXT2_MIN_DESC_SIZE_64BIT) {
> +		fs_param.s_feature_incompat |= EXT4_FEATURE_INCOMPAT_64BIT;
> +		fs_param.s_desc_size = EXT2_MIN_DESC_SIZE_64BIT;
> +	}
> +
>  	if (!force && fs_param.s_blocks_count >= ((unsigned) 1 << 31)) {
>

Why would one need variable descriptor size. Right now we have only two descriptor sizes right (32 and 64 ).  Can't we figure out
the descriptor size we should use by looking at the partition size ? What is that i am missing ?. 

-aneesh