Re: [PATCH] mke2fs: fix hugefile creation so the hugefile(s) are contiguous

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Hi Ted,

On Mon, Jun 19, 2017 at 06:49:27PM -0400, Theodore Ts'o wrote:
> Commit 4f868703f6f2: "libext2fs: use fallocate for creating journals
> and hugefiles" introduced a regression for the mke2fs hugefile
> feature.  The problem is that the fallocate library function
> intersperses the extent tree metadata blocks with the data blocks, and
> this violates the hugefile guarantee that the created files should be
> physically contiguous on disk.
> 
> Unfortuantely the m_hugefile regression test was flawed, and didn't
> pick up the regression.
> 
> This commit fixes the regression test so that it detects the problem
> before fixing mke2fs, and also fixes the mke2fs hugefile by reverting
> the mke2fs hugefile portion of commit 4f868703f6f2.
> 

Can you also update the mke2fs.conf man page to document under what
circumstances it can be assumed that the preallocated "hugefiles" will be
physically contiguous?  Currently I don't see any mention of it.

> diff --git a/misc/mk_hugefiles.c b/misc/mk_hugefiles.c
> index 5882394d..ec4e0470 100644
> --- a/misc/mk_hugefiles.c
> +++ b/misc/mk_hugefiles.c
> @@ -262,8 +262,12 @@ static errcode_t mk_hugefile(ext2_filsys fs, blk64_t num,
>  
>  {
>  	errcode_t		retval;
> +	blk64_t			lblk, bend = 0;
> +	__u64			size;
> +	blk64_t			left;
> +	blk64_t			count = 0;
>  	struct ext2_inode	inode;
> -	int			falloc_flags;
> +	ext2_extent_handle_t	handle;
>  
>  	retval = ext2fs_new_inode(fs, 0, LINUX_S_IFREG, NULL, ino);
>  	if (retval)
> @@ -283,20 +287,85 @@ static errcode_t mk_hugefile(ext2_filsys fs, blk64_t num,
>  
>  	ext2fs_inode_alloc_stats2(fs, *ino, +1, 0);
>  
> -	if (ext2fs_has_feature_extents(fs->super))
> -		inode.i_flags |= EXT4_EXTENTS_FL;
> -
> -	falloc_flags = EXT2_FALLOCATE_FORCE_INIT;
> -	if (zero_hugefile)
> -		falloc_flags |= EXT2_FALLOCATE_ZERO_BLOCKS;
> -	retval = ext2fs_fallocate(fs, falloc_flags, *ino, &inode, goal, 0, num);
> +	retval = ext2fs_extent_open2(fs, *ino, &inode, &handle);
>  	if (retval)
>  		return retval;
> -	retval = ext2fs_inode_size_set(fs, &inode, num * fs->blocksize);
> +
> +	lblk = 0;
> +	left = num ? num : 1;

Add a comment explaining why ext2fs_fallocate() isn't sufficient?

Alternatively, would it be possible to fix ext2fs_fallocate() instead?

> diff --git a/tests/m_hugefile/expect b/tests/m_hugefile/expect
> index 82a60319..aee63f90 100644
> --- a/tests/m_hugefile/expect
> +++ b/tests/m_hugefile/expect
> @@ -14,23 +14,103 @@ Pass 4: Checking reference counts
>  Pass 5: Checking group summary information
>  
>  Exit status is 0
> -debugfs -R "extents /store/big-data" test.img | head
> +debugfs -R "extents /store/big-data" test.img
>  Level Entries                 Logical                Physical Length Flags
>   0/ 2   1/  1          0 - 1073610751     131070              1073610752
>   1/ 2   1/ 97          0 -   11108351     131071              11108352
> - 2/ 2   1/339          0 -      32767     131072 -     163839  32768 
> - 2/ 2   2/339      32768 -      65535     163840 -     196607  32768 
> - 2/ 2   3/339      65536 -      98303     196608 -     229375  32768 
> - 2/ 2   4/339      98304 -     131071     229376 -     262143  32768 
> - 2/ 2   5/339     131072 -     163839     262144 -     294911  32768 
> - 2/ 2   6/339     163840 -     196607     294912 -     327679  32768 
> - 2/ 2   7/339     196608 -     229375     327680 -     360447  32768 
> - 2/ 2   8/339     229376 -     262143     360448 -     393215  32768 
> - 2/ 2   9/339     262144 -     294911     393216 -     425983  32768 
> - 2/ 2  10/339     294912 -     327679     425984 -     458751  32768 
> - 2/ 2  11/339     327680 -     360447     458752 -     491519  32768 
> - 2/ 2  12/339     360448 -     393215     491520 -     524287  32768 
> - 2/ 2  13/339     393216 -     425983     524288 -     557055  32768 
> - 2/ 2  14/339     425984 -     458751     557056 -     589823  32768 
> - 2/ 2  15/339     458752 -     491519     589824 -     622591  32768 
> - 2/ 2  16/339     491520 -     524287     622592 -     655359  32768 
> + 1/ 2   2/ 97   11108352 -   22216703      98567              11108352
> + 1/ 2   3/ 97   22216704 -   33325055      98568              11108352
> + 1/ 2   4/ 97   33325056 -   44433407      98569              11108352
> + 1/ 2   5/ 97   44433408 -   55541759      98570              11108352
> + 1/ 2   6/ 97   55541760 -   66650111      98571              11108352
> + 1/ 2   7/ 97   66650112 -   77758463      98572              11108352
> + 1/ 2   8/ 97   77758464 -   88866815      98573              11108352
> + 1/ 2   9/ 97   88866816 -   99975167      98574              11108352
> + 1/ 2  10/ 97   99975168 -  111083519      98575              11108352
> + 1/ 2  11/ 97  111083520 -  122191871      98576              11108352
> + 1/ 2  12/ 97  122191872 -  133300223      98577              11108352
> + 1/ 2  13/ 97  133300224 -  144408575      98578              11108352
> + 1/ 2  14/ 97  144408576 -  155516927      98579              11108352
> + 1/ 2  15/ 97  155516928 -  166625279      98580              11108352
> + 1/ 2  16/ 97  166625280 -  177733631      98581              11108352
> + 1/ 2  17/ 97  177733632 -  188841983      98582              11108352
> + 1/ 2  18/ 97  188841984 -  199950335      98583              11108352
> + 1/ 2  19/ 97  199950336 -  211058687      98584              11108352
> + 1/ 2  20/ 97  211058688 -  222167039      98585              11108352
> + 1/ 2  21/ 97  222167040 -  233275391      98586              11108352
> + 1/ 2  22/ 97  233275392 -  244383743      98587              11108352
> + 1/ 2  23/ 97  244383744 -  255492095      98588              11108352
> + 1/ 2  24/ 97  255492096 -  266600447      98589              11108352
> + 1/ 2  25/ 97  266600448 -  277708799      98590              11108352
> + 1/ 2  26/ 97  277708800 -  288817151      98591              11108352
> + 1/ 2  27/ 97  288817152 -  299925503      98592              11108352
> + 1/ 2  28/ 97  299925504 -  311033855      98593              11108352
> + 1/ 2  29/ 97  311033856 -  322142207      98594              11108352
> + 1/ 2  30/ 97  322142208 -  333250559      98595              11108352
> + 1/ 2  31/ 97  333250560 -  344358911      98596              11108352
> + 1/ 2  32/ 97  344358912 -  355467263      98597              11108352
> + 1/ 2  33/ 97  355467264 -  366575615      98598              11108352
> + 1/ 2  34/ 97  366575616 -  377683967      98599              11108352
> + 1/ 2  35/ 97  377683968 -  388792319      98600              11108352
> + 1/ 2  36/ 97  388792320 -  399900671      98601              11108352
> + 1/ 2  37/ 97  399900672 -  411009023      98602              11108352
> + 1/ 2  38/ 97  411009024 -  422117375      98603              11108352
> + 1/ 2  39/ 97  422117376 -  433225727      98604              11108352
> + 1/ 2  40/ 97  433225728 -  444334079      98605              11108352
> + 1/ 2  41/ 97  444334080 -  455442431      98606              11108352
> + 1/ 2  42/ 97  455442432 -  466550783      98607              11108352
> + 1/ 2  43/ 97  466550784 -  477659135      98608              11108352
> + 1/ 2  44/ 97  477659136 -  488767487      98609              11108352
> + 1/ 2  45/ 97  488767488 -  499875839      98610              11108352
> + 1/ 2  46/ 97  499875840 -  510984191      98611              11108352
> + 1/ 2  47/ 97  510984192 -  522092543      98612              11108352
> + 1/ 2  48/ 97  522092544 -  533200895      98613              11108352
> + 1/ 2  49/ 97  533200896 -  544309247      98614              11108352
> + 1/ 2  50/ 97  544309248 -  555417599      98615              11108352
> + 1/ 2  51/ 97  555417600 -  566525951      98616              11108352
> + 1/ 2  52/ 97  566525952 -  577634303      98617              11108352
> + 1/ 2  53/ 97  577634304 -  588742655      98618              11108352
> + 1/ 2  54/ 97  588742656 -  599851007      98619              11108352
> + 1/ 2  55/ 97  599851008 -  610959359      98620              11108352
> + 1/ 2  56/ 97  610959360 -  622067711      98621              11108352
> + 1/ 2  57/ 97  622067712 -  633176063      98622              11108352
> + 1/ 2  58/ 97  633176064 -  644284415      98623              11108352
> + 1/ 2  59/ 97  644284416 -  655392767      98624              11108352
> + 1/ 2  60/ 97  655392768 -  666501119      98625              11108352
> + 1/ 2  61/ 97  666501120 -  677609471      98626              11108352
> + 1/ 2  62/ 97  677609472 -  688717823      98627              11108352
> + 1/ 2  63/ 97  688717824 -  699826175      98628              11108352
> + 1/ 2  64/ 97  699826176 -  710934527      98629              11108352
> + 1/ 2  65/ 97  710934528 -  722042879      98630              11108352
> + 1/ 2  66/ 97  722042880 -  733151231      98631              11108352
> + 1/ 2  67/ 97  733151232 -  744259583      98632              11108352
> + 1/ 2  68/ 97  744259584 -  755367935      98633              11108352
> + 1/ 2  69/ 97  755367936 -  766476287      98634              11108352
> + 1/ 2  70/ 97  766476288 -  777584639      98635              11108352
> + 1/ 2  71/ 97  777584640 -  788692991      98636              11108352
> + 1/ 2  72/ 97  788692992 -  799801343      98637              11108352
> + 1/ 2  73/ 97  799801344 -  810909695      98638              11108352
> + 1/ 2  74/ 97  810909696 -  822018047      98639              11108352
> + 1/ 2  75/ 97  822018048 -  833126399      98640              11108352
> + 1/ 2  76/ 97  833126400 -  844234751      98641              11108352
> + 1/ 2  77/ 97  844234752 -  855343103      98642              11108352
> + 1/ 2  78/ 97  855343104 -  866451455      98643              11108352
> + 1/ 2  79/ 97  866451456 -  877559807      98644              11108352
> + 1/ 2  80/ 97  877559808 -  888668159      98645              11108352
> + 1/ 2  81/ 97  888668160 -  899776511      98646              11108352
> + 1/ 2  82/ 97  899776512 -  910884863      98647              11108352
> + 1/ 2  83/ 97  910884864 -  921993215      98648              11108352
> + 1/ 2  84/ 97  921993216 -  933101567      98649              11108352
> + 1/ 2  85/ 97  933101568 -  944209919      98650              11108352
> + 1/ 2  86/ 97  944209920 -  955318271      98651              11108352
> + 1/ 2  87/ 97  955318272 -  966426623      98652              11108352
> + 1/ 2  88/ 97  966426624 -  977534975      98653              11108352
> + 1/ 2  89/ 97  977534976 -  988643327      98654              11108352
> + 1/ 2  90/ 97  988643328 -  999751679      98655              11108352
> + 1/ 2  91/ 97  999751680 - 1010860031      98656              11108352
> + 1/ 2  92/ 97 1010860032 - 1021968383      98657              11108352
> + 1/ 2  93/ 97 1021968384 - 1033076735      98658              11108352
> + 1/ 2  94/ 97 1033076736 - 1044185087      98659              11108352
> + 1/ 2  95/ 97 1044185088 - 1055293439      98660              11108352
> + 1/ 2  96/ 97 1055293440 - 1066401791      98661              11108352
> + 1/ 2  97/ 97 1066401792 - 1073610751      98662              7208960

This only verifies that the extent tree blocks are in the expected locations.
How about also verifying that the file is actually physically contigious?  If
storing the full output file is too large it could be done algorithmically, e.g.
verifying that the following doesn't produce any output:

debugfs -R "dump_extents /store/big-data" test.img | awk '
BEGIN {
	expected_logical_start = 0;
	expected_physical_start = 0;
}
{
	if (NR != 1) {
		level = $1;
		sub(/\//, "", level);
		total_levels = $2;
		if (level == total_levels) {
			logical_start=$4;
			logical_end=$6;
			physical_start=$7;
			physical_end=$9;
			len = $10;

			if (logical_end + 1 - logical_start != len) {
				print "UNEXPECTED LENGTH for extent", $0;
			}
			if (physical_end + 1 - physical_start != len) {
				print "UNEXPECTED LENGTH for extent", $0;
			}

			if (logical_start != expected_logical_start) {
				print "UNEXPECTED LOGICAL DISCONTINUITY between extents:";
				print "\t", prev;
				print "\t", $0;
			}
			if (physical_start != expected_physical_start &&
				expected_logical_start != 0) {
				print "PHYSICAL DISCONTINUITY between extents:";
				print "\t", prev;
				print "\t", $0;
			}

			expected_logical_start = logical_end + 1;
			expected_physical_start = physical_end + 1;
		}
	}
	prev=$0;
}
'

(The awk script maybe can be cleaned up a bit; it's just something I hacked
together.  Also there may be a simpler way to do it.)

- Eric



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