[PATCH] e2fsprogs: add minimal resize size option

[PATCH] e2fsprogs: add minimal resize size option

[Josef Bacik]

Hello,

People wishing to make live usb disks and such are looking for a way to get the
minimum resize size for an ext fs in blocks so that they can just resize their
image to that size and do with it what they will.  This patch adds that
functionality, just pass -m option and it calculates the minimum number of
blocks the fs can be resized to.  Comments welcome, I was learning the ext disk
layout while writing this so if I've done something stupid/overly complicated
please point it out :), I've commented abundantly so hopefully my madness will
make sense.  Thank you,

Josef


diff --git a/resize/main.c b/resize/main.c
index 7c1d0c1..2f2887a 100644
--- a/resize/main.c
+++ b/resize/main.c
@@ -36,7 +36,7 @@ char *program_name, *device_name, *io_options;
 
 static void usage (char *prog)
 {
-	fprintf (stderr, _("Usage: %s [-d debug_flags] [-f] [-F] [-p] "
+	fprintf (stderr, _("Usage: %s [-d debug_flags] [-f] [-F] [-m] [-p] "
 			   "device [new_size]\n\n"), prog);
 
 	exit (1);
@@ -183,7 +183,7 @@ int main (int argc, char ** argv)
 	if (argc && *argv)
 		program_name = *argv;
 
-	while ((c = getopt (argc, argv, "d:fFhpS:")) != EOF) {
+	while ((c = getopt (argc, argv, "d:fFhmpS:")) != EOF) {
 		switch (c) {
 		case 'h':
 			usage(program_name);
@@ -197,6 +197,9 @@ int main (int argc, char ** argv)
 		case 'd':
 			flags |= atoi(optarg);
 			break;
+		case 'm':
+			flags |= RESIZE_BLOCKS_NEEDED_ONLY;
+			break;
 		case 'p':
 			flags |= RESIZE_PERCENT_COMPLETE;
 			break;
@@ -340,6 +343,13 @@ int main (int argc, char ** argv)
 		exit(1);
 	}
 	if (new_size_str) {
+		if (flags & RESIZE_BLOCKS_NEEDED_ONLY) {
+			com_err(program_name, 0,
+				"specifying a new size when asking for "
+				"minimal size");
+			exit(1);
+		}
+
 		new_size = parse_num_blocks(new_size_str, 
 					    fs->super->s_log_block_size);
 		if (!new_size) {
@@ -347,7 +357,7 @@ int main (int argc, char ** argv)
 				new_size_str);
 			exit(1);
 		}
-	} else {
+	} else if (!(flags & RESIZE_BLOCKS_NEEDED_ONLY)) {
 		new_size = max_size;
 		/* Round down to an even multiple of a pagesize */
 		if (sys_page_size > fs->blocksize)
@@ -392,7 +402,8 @@ int main (int argc, char ** argv)
 			"long.  Nothing to do!\n\n"), new_size);
 		exit(0);
 	}
-	if (mount_flags & EXT2_MF_MOUNTED) {
+	if ((mount_flags & EXT2_MF_MOUNTED) &&
+	    !(flags & RESIZE_BLOCKS_NEEDED_ONLY)) {
 		retval = online_resize_fs(fs, mtpt, &new_size, flags);
 	} else {
 		if (!force && ((fs->super->s_lastcheck < fs->super->s_mtime) ||
@@ -403,23 +414,28 @@ int main (int argc, char ** argv)
 				device_name);
 			exit(1);
 		}
-	printf("Resizing the filesystem on %s to %u (%dk) blocks.\n",
-		       device_name, new_size, fs->blocksize / 1024);
+		if (!(flags & RESIZE_BLOCKS_NEEDED_ONLY))
+			printf("Resizing the filesystem on %s to %u (%dk) "
+			       "blocks.\n", device_name, new_size,
+			       fs->blocksize / 1024);
 		retval = resize_fs(fs, &new_size, flags,
 				   ((flags & RESIZE_PERCENT_COMPLETE) ?
 				    resize_progress_func : 0));
 	}
+
 	if (retval) {
 		com_err(program_name, retval, _("while trying to resize %s"),
 			device_name);
 		ext2fs_close (fs);
 		exit(1);
 	}
-	printf(_("The filesystem on %s is now %u blocks long.\n\n"),
-	       device_name, new_size);
 
-	if ((st_buf.st_size > new_file_size) &&
-	    (fd > 0)) {
+	if (!(flags & RESIZE_BLOCKS_NEEDED_ONLY))
+		printf(_("The filesystem on %s is now %u blocks long.\n\n"),
+		       device_name, new_size);
+
+	if ((st_buf.st_size > new_file_size) && (fd > 0) &&
+	    !(flags & RESIZE_BLOCKS_NEEDED_ONLY)) {
 #ifdef HAVE_FSTAT64
 		ftruncate64(fd, new_file_size);
 #else
diff --git a/resize/resize2fs.c b/resize/resize2fs.c
index 9959671..ae0cb8d 100644
--- a/resize/resize2fs.c
+++ b/resize/resize2fs.c
@@ -63,7 +63,9 @@ static errcode_t ext2fs_calculate_summary_stats(ext2_filsys fs);
 				 ((blk) < (FS_INODE_TB((fs), (i)) + \
 					   (fs)->inode_blocks_per_group)))
 
-
+#define META_OVERHEAD(fs) (2 + (fs)->inode_blocks_per_group)
+#define SUPER_OVERHEAD(fs) (1 + (fs)->desc_blocks +\
+			    (fs)->super->s_reserved_gdt_blocks)
 
 /*
  * This is the top-level routine which does the dirty deed....
@@ -79,7 +81,156 @@ errcode_t resize_fs(ext2_filsys fs, blk_t *new_size, int flags,
 	retval = ext2fs_read_bitmaps(fs);
 	if (retval)
 		return retval;
-	
+
+	/*
+	 * since we only want to figure out the minimum number of blocks this
+	 * fs can be resized to, figure out the minimum number of blocks needed
+	 * to handle the metadata and reset new_size to that
+	 */
+	if (flags & RESIZE_BLOCKS_NEEDED_ONLY) {
+		blk_t inode_count, blks_needed, groups, blk, data_blocks;
+		blk_t grp, data_needed, last_start, tmp = 0;
+		int overhead = 0, old_group = -1, num_of_superblocks = 0;
+
+		/*
+		 * first figure out how many group descriptors we need to
+		 * handle the number of inodes we have
+		 */
+		inode_count = fs->super->s_inodes_count -
+			fs->super->s_free_inodes_count;
+		blks_needed = ext2fs_div_ceil(inode_count,
+						fs->super->s_inodes_per_group)
+			* EXT2_BLOCKS_PER_GROUP(fs->super);
+		groups = ext2fs_div_ceil(blks_needed,
+					 EXT2_BLOCKS_PER_GROUP(fs->super));
+
+		/*
+		 * we need to figure out how many backup superblocks we have
+		 * so we can account for that in the metadata
+		 */
+		for (grp = 0; grp < fs->group_desc_count; grp++) {
+			if (ext2fs_bg_has_super(fs, grp))
+				num_of_superblocks++;
+		}
+
+		/* calculate how many blocks are needed for data */
+		data_needed = fs->super->s_blocks_count -
+			fs->super->s_free_blocks_count;
+		data_needed -= SUPER_OVERHEAD(fs) * num_of_superblocks;
+		data_needed -= META_OVERHEAD(fs) * fs->group_desc_count;
+
+
+		/*
+		 * figure out how many data blocks we have given the number
+		 * of groups we need for our inodes
+		 */
+		data_blocks = groups * EXT2_BLOCKS_PER_GROUP(fs->super);
+		last_start = 0;
+		for (grp = 0; grp < groups; grp++) {
+			overhead = META_OVERHEAD(fs);
+
+			if (ext2fs_bg_has_super(fs, grp))
+				overhead += SUPER_OVERHEAD(fs);
+
+			/*
+			 * we want to keep track of how much data we can store
+			 * in the groups leading up to the last group so we
+			 * can determine how big the last group needs to be
+			 */
+			if (grp != (groups - 1))
+				last_start += EXT2_BLOCKS_PER_GROUP(fs->super)
+					- overhead;
+
+			data_blocks -= overhead;
+		}
+
+		/*
+		 * if we need more group descriptors in order to accomodate
+		 * our data then we need to add them here
+		 */
+		while (data_needed > data_blocks) {
+			blk_t remainder = data_needed - data_blocks;
+			blk_t extra_grps;
+
+			/*
+			 * figure out how many more groups we need for the data
+			 */
+			extra_grps = ext2fs_div_ceil(remainder,
+				EXT2_BLOCKS_PER_GROUP(fs->super));
+
+			data_blocks += extra_grps *
+				EXT2_BLOCKS_PER_GROUP(fs->super);
+
+			/* ok we have to account for the last group */
+			overhead = META_OVERHEAD(fs);
+			if (ext2fs_bg_has_super(fs, groups-1))
+				overhead += SUPER_OVERHEAD(fs);
+			last_start += EXT2_BLOCKS_PER_GROUP(fs->super) -
+				overhead;
+
+			for (grp = groups; grp < groups+extra_grps; grp++) {
+				overhead = META_OVERHEAD(fs);
+				if (ext2fs_bg_has_super(fs, grp))
+					overhead += SUPER_OVERHEAD(fs);
+
+				/*
+				 * again, we need to see how much data we cram
+				 * into all the groups leading up to the last
+				 * group
+				 */
+				if (grp != (groups + extra_grps - 1)) {
+					last_start +=
+						EXT2_BLOCKS_PER_GROUP(fs->super)
+						- overhead;
+				}
+
+				data_blocks -= overhead;
+			}
+
+			groups += extra_grps;
+		}
+
+		/* now for the fun voodoo */
+		overhead = META_OVERHEAD(fs);
+
+		/*
+		 * if this is the case then the last group is going to have
+		 * data in it so we need to adjust the size of the last group
+		 * accordingly
+		 */
+		if (last_start < data_needed) {
+			blk_t remainder = data_needed - last_start;
+
+			/*
+			 * 50 is a magic number that mkfs/resize uses to
+			 * see if its even worth making/resizing the fs.
+			 * basically you need to have at least 50 blocks in
+			 * addition to the blocks needed for the metadata in
+			 * the last group
+			 */
+			if (remainder > 50)
+				overhead += remainder;
+			else
+				overhead += 50;
+		} else
+			overhead += 50;
+
+		if (ext2fs_bg_has_super(fs, groups-1))
+			overhead += SUPER_OVERHEAD(fs);
+
+		/*
+		 * since our last group doesn't have to be BLOCKS_PER_GROUP
+		 * larg, we only do groups-1, and then add the number of blocks
+		 * needed to handle the group descriptor metadata+data that we
+		 * need
+		 */
+		blks_needed = (groups-1) * EXT2_BLOCKS_PER_GROUP(fs->super);
+		blks_needed += overhead;
+
+		printf("Minimum resize size in blocks is %d\n", blks_needed);
+		return 0;
+	}
+
 	/*
 	 * Create the data structure
 	 */
@@ -90,7 +241,7 @@ errcode_t resize_fs(ext2_filsys fs, blk_t *new_size, int flags,
 
 	rfs->old_fs = fs;
 	rfs->flags = flags;
-	rfs->itable_buf	 = 0;
+	rfs->itable_buf = 0;
 	rfs->progress = progress;
 	retval = ext2fs_dup_handle(fs, &rfs->new_fs);
 	if (retval)
@@ -113,7 +264,7 @@ errcode_t resize_fs(ext2_filsys fs, blk_t *new_size, int flags,
 		       rfs->new_fs->super->s_free_blocks_count,
 		       rfs->needed_blocks);
 #endif
-	
+
 	retval = block_mover(rfs);
 	if (retval)
 		goto errout;
diff --git a/resize/resize2fs.h b/resize/resize2fs.h
index f87d04e..cf42a62 100644
--- a/resize/resize2fs.h
+++ b/resize/resize2fs.h
@@ -79,6 +79,7 @@ typedef struct ext2_sim_progress *ext2_sim_progmeter;
 
 #define RESIZE_PERCENT_COMPLETE		0x0100
 #define RESIZE_VERBOSE			0x0200
+#define RESIZE_BLOCKS_NEEDED_ONLY	0x0400
 
 /*
  * The core state structure for the ext2 resizer
@@ -127,7 +128,7 @@ extern errcode_t resize_fs(ext2_filsys fs, blk_t *new_size, int flags,
 					    int pass, unsigned long cur,
 					    unsigned long max));
 
-extern errcode_t adjust_fs_info(ext2_filsys fs, ext2_filsys old_fs, 
+extern errcode_t adjust_fs_info(ext2_filsys fs, ext2_filsys old_fs,
 				blk_t new_size);
 
 

Re: [PATCH] e2fsprogs: add minimal resize size option

[Theodore Tso]

On Wed, Jan 02, 2008 at 03:16:59PM -0500, Josef Bacik wrote:
> Hello,
> 
> People wishing to make live usb disks and such are looking for a way
> to get the minimum resize size for an ext fs in blocks so that they
> can just resize their image to that size and do with it what they
> will.  This patch adds that functionality, just pass -m option and
> it calculates the minimum number of blocks the fs can be resized to.

Three comments.  Instead of using a new option, why not simply let
resize2fs check to see if the optional parameter is something like
"min" or "0"?

Secondly, I'd suggest factoring out the calculation of the minimal
size into a separate function.

Finally, please don't fix whitespace issues, as it makes it harder for me
to merge between the "maint" and "master" development lines.  What I
plan to do is to do a massive fixup of trailing whitespace before the
next major (1.41) release of e2fsprogs.  Any new lines added by
patches should not introduce any new trailing whitespace, of course.

Thanks!

						- Ted

Re: [PATCH] e2fsprogs: add minimal resize size option

[Josef Bacik]

On Thu, Jan 03, 2008 at 12:21:01PM -0500, Theodore Tso wrote:
> On Wed, Jan 02, 2008 at 03:16:59PM -0500, Josef Bacik wrote:
> > Hello,
> > 
> > People wishing to make live usb disks and such are looking for a way
> > to get the minimum resize size for an ext fs in blocks so that they
> > can just resize their image to that size and do with it what they
> > will.  This patch adds that functionality, just pass -m option and
> > it calculates the minimum number of blocks the fs can be resized to.
> 
> Three comments.  Instead of using a new option, why not simply let
> resize2fs check to see if the optional parameter is something like
> "min" or "0"?
> 
> Secondly, I'd suggest factoring out the calculation of the minimal
> size into a separate function.
> 
> Finally, please don't fix whitespace issues, as it makes it harder for me
> to merge between the "maint" and "master" development lines.  What I
> plan to do is to do a massive fixup of trailing whitespace before the
> next major (1.41) release of e2fsprogs.  Any new lines added by
> patches should not introduce any new trailing whitespace, of course.
>

Hmm sorry about the whitespace things, I thought I had cleaned all those up.
Thanks much for the suggestions, here is the updated patch with your suggestions
implemented, if you pass a size of 0 it will just spit out the minimum resize
size.  Thanks much,

Josef

 
diff --git a/resize/main.c b/resize/main.c
index 7c1d0c1..44d05b0 100644
--- a/resize/main.c
+++ b/resize/main.c
@@ -342,11 +342,8 @@ int main (int argc, char ** argv)
 	if (new_size_str) {
 		new_size = parse_num_blocks(new_size_str, 
 					    fs->super->s_log_block_size);
-		if (!new_size) {
-			com_err(program_name, 0, _("bad filesystem size - %s"),
-				new_size_str);
-			exit(1);
-		}
+		if (!new_size)
+			flags |= RESIZE_BLOCKS_NEEDED_ONLY;
 	} else {
 		new_size = max_size;
 		/* Round down to an even multiple of a pagesize */
@@ -392,7 +389,8 @@ int main (int argc, char ** argv)
 			"long.  Nothing to do!\n\n"), new_size);
 		exit(0);
 	}
-	if (mount_flags & EXT2_MF_MOUNTED) {
+	if ((mount_flags & EXT2_MF_MOUNTED) &&
+	    !(flags & RESIZE_BLOCKS_NEEDED_ONLY)) {
 		retval = online_resize_fs(fs, mtpt, &new_size, flags);
 	} else {
 		if (!force && ((fs->super->s_lastcheck < fs->super->s_mtime) ||
@@ -403,8 +401,10 @@ int main (int argc, char ** argv)
 				device_name);
 			exit(1);
 		}
-	printf("Resizing the filesystem on %s to %u (%dk) blocks.\n",
-		       device_name, new_size, fs->blocksize / 1024);
+		if (!(flags & RESIZE_BLOCKS_NEEDED_ONLY))
+			printf("Resizing the filesystem on %s to %u (%dk) "
+			       "blocks.\n", device_name, new_size,
+			       fs->blocksize / 1024);
 		retval = resize_fs(fs, &new_size, flags,
 				   ((flags & RESIZE_PERCENT_COMPLETE) ?
 				    resize_progress_func : 0));
@@ -415,11 +415,13 @@ int main (int argc, char ** argv)
 		ext2fs_close (fs);
 		exit(1);
 	}
-	printf(_("The filesystem on %s is now %u blocks long.\n\n"),
-	       device_name, new_size);
 
-	if ((st_buf.st_size > new_file_size) &&
-	    (fd > 0)) {
+	if (!(flags & RESIZE_BLOCKS_NEEDED_ONLY))
+		printf(_("The filesystem on %s is now %u blocks long.\n\n"),
+		       device_name, new_size);
+
+	if ((st_buf.st_size > new_file_size) && (fd > 0) &&
+	    !(flags & RESIZE_BLOCKS_NEEDED_ONLY)) {
 #ifdef HAVE_FSTAT64
 		ftruncate64(fd, new_file_size);
 #else
diff --git a/resize/resize2fs.c b/resize/resize2fs.c
index 9959671..ad50c30 100644
--- a/resize/resize2fs.c
+++ b/resize/resize2fs.c
@@ -48,7 +48,7 @@ static errcode_t inode_ref_fix(ext2_resize_t rfs);
 static errcode_t move_itables(ext2_resize_t rfs);
 static errcode_t fix_resize_inode(ext2_filsys fs);
 static errcode_t ext2fs_calculate_summary_stats(ext2_filsys fs);
-
+static errcode_t ext2fs_calculate_minimum_resize_size(ext2_filsys fs);
 /*
  * Some helper CPP macros
  */
@@ -63,7 +63,9 @@ static errcode_t ext2fs_calculate_summary_stats(ext2_filsys fs);
 				 ((blk) < (FS_INODE_TB((fs), (i)) + \
 					   (fs)->inode_blocks_per_group)))
 
-
+#define META_OVERHEAD(fs) (2 + (fs)->inode_blocks_per_group)
+#define SUPER_OVERHEAD(fs) (1 + (fs)->desc_blocks +\
+			    (fs)->super->s_reserved_gdt_blocks)
 
 /*
  * This is the top-level routine which does the dirty deed....
@@ -80,6 +82,9 @@ errcode_t resize_fs(ext2_filsys fs, blk_t *new_size, int flags,
 	if (retval)
 		return retval;
 	
+	if (flags & RESIZE_BLOCKS_NEEDED_ONLY)
+		return ext2fs_calculate_minimum_resize_size(fs);
+
 	/*
 	 * Create the data structure
 	 */
@@ -1628,3 +1633,141 @@ static errcode_t ext2fs_calculate_summary_stats(ext2_filsys fs)
 	ext2fs_mark_super_dirty(fs);
 	return 0;
 }
+
+/*
+ * calcluate the minimum number of blocks the given fs can be resized to
+ */
+static errcode_t ext2fs_calculate_minimum_resize_size(ext2_filsys fs)
+{
+	blk_t inode_count, blks_needed, groups, blk, data_blocks;
+	blk_t grp, data_needed, last_start;
+	int overhead = 0, old_group = -1, num_of_superblocks = 0;
+
+	/*
+	 * first figure out how many group descriptors we need to
+	 * handle the number of inodes we have
+	 */
+	inode_count = fs->super->s_inodes_count -
+		fs->super->s_free_inodes_count;
+	blks_needed = ext2fs_div_ceil(inode_count,
+				      fs->super->s_inodes_per_group) *
+		EXT2_BLOCKS_PER_GROUP(fs->super);
+	groups = ext2fs_div_ceil(blks_needed,
+				 EXT2_BLOCKS_PER_GROUP(fs->super));
+
+	/*
+	 * we need to figure out how many backup superblocks we have so we can
+	 * account for that in the metadata
+	 */
+	for (grp = 0; grp < fs->group_desc_count; grp++) {
+		if (ext2fs_bg_has_super(fs, grp))
+			num_of_superblocks++;
+	}
+
+	/* calculate how many blocks are needed for data */
+	data_needed = fs->super->s_blocks_count -
+		fs->super->s_free_blocks_count;
+	data_needed -= SUPER_OVERHEAD(fs) * num_of_superblocks;
+	data_needed -= META_OVERHEAD(fs) * fs->group_desc_count;
+
+	/*
+	 * figure out how many data blocks we have given the number of groups
+	 * we need for our inodes
+	 */
+	data_blocks = groups * EXT2_BLOCKS_PER_GROUP(fs->super);
+	last_start = 0;
+	for (grp = 0; grp < groups; grp++) {
+		overhead = META_OVERHEAD(fs);
+
+		if (ext2fs_bg_has_super(fs, grp))
+			overhead += SUPER_OVERHEAD(fs);
+
+		/*
+		 * we want to keep track of how much data we can store in
+		 * the groups leading up to the last group so we can determine
+		 * how big the last group needs to be
+		 */
+		if (grp != (groups - 1))
+			last_start += EXT2_BLOCKS_PER_GROUP(fs->super) -
+				overhead;
+
+		data_blocks -= overhead;
+	}
+
+	/*
+	 * if we need more group descriptors in order to accomodate our data
+	 * then we need to add them here
+	 */
+	while (data_needed > data_blocks) {
+		blk_t remainder = data_needed - data_blocks;
+		blk_t extra_grps;
+
+		/* figure out how many more groups we need for the data */
+		extra_grps = ext2fs_div_ceil(remainder,
+					     EXT2_BLOCKS_PER_GROUP(fs->super));
+
+		data_blocks += extra_grps * EXT2_BLOCKS_PER_GROUP(fs->super);
+
+		/* ok we have to account for the last group */
+		overhead = META_OVERHEAD(fs);
+		if (ext2fs_bg_has_super(fs, groups-1))
+			overhead += SUPER_OVERHEAD(fs);
+		last_start += EXT2_BLOCKS_PER_GROUP(fs->super) - overhead;
+
+		for (grp = groups; grp < groups+extra_grps; grp++) {
+			overhead = META_OVERHEAD(fs);
+			if (ext2fs_bg_has_super(fs, grp))
+				overhead += SUPER_OVERHEAD(fs);
+
+			/*
+			 * again, we need to see how much data we cram into
+			 * all of the groups leading up to the last group
+			 */
+			if (grp != (groups + extra_grps - 1))
+				last_start += EXT2_BLOCKS_PER_GROUP(fs->super)
+					- overhead;
+
+			data_blocks -= overhead;
+		}
+
+		groups += extra_grps;
+	}
+
+	/* now for the fun voodoo */
+	overhead = META_OVERHEAD(fs);
+
+	/*
+	 * if this is the case then the last group is going to have data in it
+	 * so we need to adjust the size of the last group accordingly
+	 */
+	if (last_start < data_needed) {
+		blk_t remainder = data_needed - last_start;
+
+		/*
+		 * 50 is a magic number that mkfs/resize uses to see if its
+		 * even worth making/resizing the fs.  basically you need to
+		 * have at least 50 blocks in addition to the blocks needed
+		 * for the metadata in the last group
+		 */
+		if (remainder > 50)
+			overhead += remainder;
+		else
+			overhead += 50;
+	} else
+		overhead += 50;
+
+	if (ext2fs_bg_has_super(fs, groups-1))
+		overhead += SUPER_OVERHEAD(fs);
+
+	/*
+	 * since our last group doesn't have to be BLOCKS_PER_GROUP large, we
+	 * only do groups-1, and then add the number of blocks needed to
+	 * handle the group descriptor metadata+data that we need
+	 */
+	blks_needed = (groups-1) * EXT2_BLOCKS_PER_GROUP(fs->super);
+	blks_needed += overhead;
+
+	printf("Minimum resize size in blocks is %d\n", blks_needed);
+
+	return 0;
+}
diff --git a/resize/resize2fs.h b/resize/resize2fs.h
index f87d04e..14a2c3f 100644
--- a/resize/resize2fs.h
+++ b/resize/resize2fs.h
@@ -79,6 +79,7 @@ typedef struct ext2_sim_progress *ext2_sim_progmeter;
 
 #define RESIZE_PERCENT_COMPLETE		0x0100
 #define RESIZE_VERBOSE			0x0200
+#define RESIZE_BLOCKS_NEEDED_ONLY	0x0400
 
 /*
  * The core state structure for the ext2 resizer

Re: [PATCH] e2fsprogs: add minimal resize size option

[Eric Sandeen]

Theodore Tso wrote:
> On Wed, Jan 02, 2008 at 03:16:59PM -0500, Josef Bacik wrote:
>> Hello,
>>
>> People wishing to make live usb disks and such are looking for a way
>> to get the minimum resize size for an ext fs in blocks so that they
>> can just resize their image to that size and do with it what they
>> will.  This patch adds that functionality, just pass -m option and
>> it calculates the minimum number of blocks the fs can be resized to.
> 
> Three comments.  Instead of using a new option, why not simply let
> resize2fs check to see if the optional parameter is something like
> "min" or "0"?

How about spitting out minimum size message whenever a too-small size is
specified; 0 would then of course always take no action, but simply
print the minimum.  For a size that's actually specified, but too small,
it'd still be useful I think, to say "XXXXX blocks is too small, minimum
size is YYYYY" ?

0 could be special-cased to not print the "0 blocks is too small" part
(or whatever...)

-Eric