Date:   Thu, 28 Jun 2018 13:26:11 -0600
From:   Andreas Dilger <adilger@...ger.ca>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>,
        c17828 <artem.blagodarenko@...il.com>
Cc:     Ext4 Developers List <linux-ext4@...r.kernel.org>,
        Alexey Lyashkov <alexey.lyashkov@...il.com>
Subject: Re: [PATCH] filefrag: Lustre changes to filefrag FIEMAP handling

On Jun 28, 2018, at 8:06 AM, Darrick J. Wong <darrick.wong@...cle.com> wrote:
> 
> On Wed, Jun 27, 2018 at 06:57:31PM +0300, c17828 wrote:
>> From: Andreas Dilger <andreas.dilger@...el.com>
>> 
>> Add support for multiple-device filesystems by defining a new
>> fe_device field in the fiemap_extent structure.  This allows
>> printing the filesystem-relative or linux block device number
>> associated with each extent of a file.  If a single filesystem
>> extent is mirrored to multiple block devices, the fe_device
>> field can be used to disambiguate the multiple copies.
>> 
>> If the "-l" (device-logical) option is given to filefrag, then
>> all extents for a particular device of a file are returned
>> before returning extents for the next device.  This makes it
>> easier to see if extent allocation within a single device is
>> contiguous, instead of returning all of the blocks of a file
>> interleaved in file-logical-offset order.
>> 
>> Change-Id: Icdefe4dbc319e6652c3d6641e1500f2cfaf63605
>> Signed-off-by: Andreas Dilger <andreas.dilger@...el.com>
>> Signed-off-by: Artem Blagodarenko <artem.blagodarenko@...il.com>
>> ---
>> lib/ext2fs/fiemap.h |  7 +++++-
>> misc/filefrag.8.in  |  5 +++-
>> misc/filefrag.c     | 67 +++++++++++++++++++++++++++++++++++++++++++----------
>> 3 files changed, 65 insertions(+), 14 deletions(-)
>> 
>> diff --git a/lib/ext2fs/fiemap.h b/lib/ext2fs/fiemap.h
>> index a331bc12..261a0b2b 100644
>> --- a/lib/ext2fs/fiemap.h
>> +++ b/lib/ext2fs/fiemap.h
>> @@ -19,7 +19,8 @@ struct fiemap_extent {
>> 	__u64 fe_length;   /* length in bytes for this extent */
>> 	__u64 fe_reserved64[2];
>> 	__u32 fe_flags;    /* FIEMAP_EXTENT_* flags for this extent */
>> -	__u32 fe_reserved[3];
>> +	__u32 fe_device;   /* device number (fs-specific if FIEMAP_EXTENT_NET)*/
>> +	__u32 fe_reserved[2];
>> };
>> 
>> struct fiemap {
>> @@ -42,6 +43,7 @@ struct fiemap {
>> 
>> #define FIEMAP_FLAG_SYNC	0x00000001 /* sync file data before map */
>> #define FIEMAP_FLAG_XATTR	0x00000002 /* map extended attribute tree */
>> +#define FIEMAP_FLAG_DEVICE_ORDER 0x40000000 /* return device ordered mapping */
>> 
>> #define FIEMAP_FLAGS_COMPAT	(FIEMAP_FLAG_SYNC | FIEMAP_FLAG_XATTR)
>> 
>> @@ -67,4 +69,7 @@ struct fiemap {
>> #define FIEMAP_EXTENT_SHARED		0x00002000 /* Space shared with other
>> 						    * files. */
>> 
>> +/* Network filesystem flags - use a high bit, don't conflict with upstream */
>> +#define FIEMAP_EXTENT_NET		0x80000000 /* Data stored remotely. */
> 
> Why does "NET" means "look for a device number"?

These are two semi-independent changes, but both are needed for filefrag to work
with Lustre.

The fe_device field is used to store the server "device" number for each extent,
so that it is possible to determine whether blocks are stored on the same server
or not.

The "FIEMAP_EXTENT_NET" flag means "the data is stored on a different system,
don't bother trying to access it from the local block device (this was intended
to be for things like LILO that access blocks directly from disk after mapping).

The "FIEMAP_FLAG_DEVICE_ORDER" flag is a request for multi-device files that the
blocks are returned in offset order for each device first, rather than being
interleaved across devices.  For Lustre, files may be striped RAID-0 style across
servers in 1MB (or 4MB, whatever) chunks.  If they are returned strictly in file
offset order then the maximum extent size would be only 1MB, which may result in
many thousands of extents being returned, and hides the fact that the extents are
allocated contiguously on disk at the server.  Returning the extents in device
order first (essentially per-ext4-filesystem order) results in normal FIEMAP
extents being displayed by filefrag.

Since "device_offset"/DEVICE_ORDER is only set for Lustre filesystems, it shouldn't
make any difference to normal usage, and even then it will try without that flag if
the kernel returns an error.

> What's the format for fe_device?  Arbitrary 32-bit cookie?  Kernel
> dev_t?  Something else?

For most filesystems I'd imagine it will be a 32-bit kernel dev_t, which will be
useful for Btrfs and XFS that handle multiple block devices.  For Lustre ("NET")
extents it is the server index within the filesystem (0-thousands) but it can be
considered a cookie, since it just needs to be unique among the devices (we may
need to split it into server and device parts if we start handling multi-device
filesystems on the server).

> Is there a corresponding change for include/uapi/linux/fiemap.h?  Would
> be nice if we could wire that up to iomap_fiemap <hint hint>

I don't have a patch for this ready yet.  Artem, is that something you are
looking at?  It would be useful for both XFS (real-time volume) and Btrfs, since
they are using multiple block devices for storage.  I guess I missed my chance
to use Lustre as the in-tree user of this field... :-/

Cheers, Andreas

>> +
>> #endif /* _LINUX_FIEMAP_H */
>> diff --git a/misc/filefrag.8.in b/misc/filefrag.8.in
>> index 292b3b7d..fdba67f7 100644
>> --- a/misc/filefrag.8.in
>> +++ b/misc/filefrag.8.in
>> @@ -8,7 +8,7 @@ filefrag \- report on file fragmentation
>> .BI \-b blocksize
>> ]
>> [
>> -.B \-BeksvxX
>> +.B \-BeklsvxX
>> ]
>> [
>> .I files...
>> @@ -46,6 +46,9 @@ Print output in extent format, even for block-mapped files.
>> .BI \-k
>> Use 1024\-byte blocksize for output (identical to '\-b 1024').
>> .TP
>> +.B \-l
>> +Extents are displayed in device-logical offset order.
>> +.TP
>> .B \-s
>> Sync the file before requesting the mapping.
>> .TP
>> diff --git a/misc/filefrag.c b/misc/filefrag.c
>> index 9c57ab93..78e13076 100644
>> --- a/misc/filefrag.c
>> +++ b/misc/filefrag.c
>> @@ -54,14 +54,16 @@ int verbose = 0;
>> int blocksize;		/* Use specified blocksize (default 1kB) */
>> int sync_file = 0;	/* fsync file before getting the mapping */
>> int xattr_map = 0;	/* get xattr mapping */
>> -int force_bmap;	/* force use of FIBMAP instead of FIEMAP */
>> +int force_bmap;		/* force use of FIBMAP instead of FIEMAP */
>> int force_extent;	/* print output in extent format always */
>> +int device_offset;	/* extents report device-relative offsets */
>> int logical_width = 8;
>> int physical_width = 10;
>> const char *ext_fmt = "%4d: %*llu..%*llu: %*llu..%*llu: %6llu: %s\n";
>> const char *hex_fmt = "%4d: %*llx..%*llx: %*llx..%*llx: %6llx: %s\n";
>> 
>> -#define FILEFRAG_FIEMAP_FLAGS_COMPAT (FIEMAP_FLAG_SYNC | FIEMAP_FLAG_XATTR)
>> +#define FILEFRAG_FIEMAP_FLAGS_COMPAT (FIEMAP_FLAG_SYNC | FIEMAP_FLAG_XATTR |\
>> +				      FIEMAP_FLAG_DEVICE_ORDER)
>> 
>> #define FIBMAP		_IO(0x00, 1)	/* bmap access */
>> #define FIGETBSZ	_IO(0x00, 2)	/* get the block size used for bmap */
>> @@ -120,10 +122,10 @@ static void print_extent_header(void)
>> {
>> 	printf(" ext: %*s %*s length: %*s flags:\n",
>> 	       logical_width * 2 + 3,
>> -	       "logical_offset:",
>> +	       device_offset ? "device_logical:" : "logical_offset:",
>> 	       physical_width * 2 + 3, "physical_offset:",
>> -	       physical_width + 1,
>> -	       "expected:");
>> +	       device_offset ? 5 : physical_width + 1,
>> +	       device_offset ? " dev:" : "expected:");
>> }
>> 
>> static void print_flag(__u32 *flags, __u32 mask, char *buf, const char *name)
>> @@ -159,11 +161,11 @@ static void print_extent_info(struct fiemap_extent *fm_extent, int cur_ex,
>> 		physical_blk = fm_extent->fe_physical >> blk_shift;
>> 	}
>> 
>> -	if (expected)
>> -		sprintf(flags, ext_fmt == hex_fmt ? "%*llx: " : "%*llu: ",
>> +	if (device_offset)
>> +		sprintf(flags, "%04x: ", fm_extent->fe_device);
>> +	else if (expected)
>> +		sprintf(flags, ext_fmt == hex_fmt ? "%*llx:" : "%*llu: ",
>> 			physical_width, expected >> blk_shift);
>> -	else
>> -		sprintf(flags, "%.*s  ", physical_width, "                   ");
>> 
>> 	fe_flags = fm_extent->fe_flags;
>> 	print_flag(&fe_flags, FIEMAP_EXTENT_LAST, flags, "last,");
>> @@ -177,6 +179,8 @@ static void print_extent_info(struct fiemap_extent *fm_extent, int cur_ex,
>> 	print_flag(&fe_flags, FIEMAP_EXTENT_UNWRITTEN, flags, "unwritten,");
>> 	print_flag(&fe_flags, FIEMAP_EXTENT_MERGED, flags, "merged,");
>> 	print_flag(&fe_flags, FIEMAP_EXTENT_SHARED, flags, "shared,");
>> +	print_flag(&fe_flags, FIEMAP_EXTENT_NET, flags, "net,");
>> +
>> 	/* print any unknown flags as hex values */
>> 	for (mask = 1; fe_flags != 0 && mask != 0; mask <<= 1) {
>> 		char hex[6];
>> @@ -217,6 +221,7 @@ static int filefrag_fiemap(int fd, int blk_shift, int *num_extents,
>> 	unsigned int i;
>> 	int fiemap_header_printed = 0;
>> 	int tot_extents = 0, n = 0;
>> +	int previous_device = 0;
>> 	int last = 0;
>> 	int rc;
>> 
>> @@ -228,6 +233,12 @@ static int filefrag_fiemap(int fd, int blk_shift, int *num_extents,
>> 	if (xattr_map)
>> 		flags |= FIEMAP_FLAG_XATTR;
>> 
>> +	if (device_offset) {
>> +		flags |= FIEMAP_FLAG_DEVICE_ORDER;
>> +		memset(fm_ext, 0, sizeof(struct fiemap_extent));
>> +	}
>> +
>> +retry_wo_device_order:
>> 	do {
>> 		fiemap->fm_length = ~0ULL;
>> 		fiemap->fm_flags = flags;
>> @@ -242,6 +253,10 @@ static int filefrag_fiemap(int fd, int blk_shift, int *num_extents,
>> 						"flags %x\n",
>> 				       fiemap->fm_flags);
>> 				fiemap_incompat_printed = 1;
>> +			} else if (rc == EBADR && (fiemap->fm_flags &
>> +						   FIEMAP_FLAG_DEVICE_ORDER)) {
>> +				flags &= ~FIEMAP_FLAG_DEVICE_ORDER;
>> +				goto retry_wo_device_order;
>> 			}
>> 			return rc;
>> 		}
>> @@ -260,6 +275,9 @@ static int filefrag_fiemap(int fd, int blk_shift, int *num_extents,
>> 					 fm_last.fe_length;
>> 			expected = fm_last.fe_physical +
>> 				   fm_ext[i].fe_logical - fm_last.fe_logical;
>> +			if (previous_device != fm_ext[i].fe_device)
>> +				previous_device = fm_ext[i].fe_device;
>> +
>> 			if (fm_ext[i].fe_logical != 0 &&
>> 			    fm_ext[i].fe_physical != expected &&
>> 			    fm_ext[i].fe_physical != expected_dense) {
>> @@ -278,8 +296,20 @@ static int filefrag_fiemap(int fd, int blk_shift, int *num_extents,
>> 			n++;
>> 		}
>> 
>> -		fiemap->fm_start = (fm_ext[i - 1].fe_logical +
>> -				    fm_ext[i - 1].fe_length);
>> +		/* For DEVICE_ORDER mappings, if EXTENT_LAST not yet found then
>> +		 * fm_start needs to be the same as it was for earlier ioctl.
>> +		 * The first extent is used to pass the end offset and device
>> +		 * of the last FIEMAP call.  Otherwise, we ask for extents
>> +		 * starting from where the last mapping ended. */
>> +		if (flags & FIEMAP_FLAG_DEVICE_ORDER) {
>> +			fm_ext[0].fe_logical =	fm_ext[i - 1].fe_logical +
>> +						fm_ext[i - 1].fe_length;
>> +			fm_ext[0].fe_device =	fm_ext[i - 1].fe_device;
>> +			fiemap->fm_start =	0;
>> +		} else {
>> +			fiemap->fm_start =	fm_ext[i - 1].fe_logical +
>> +						fm_ext[i - 1].fe_length;
>> +		}
>> 	} while (last == 0);
>> 
>> 	*num_extents = tot_extents;
>> @@ -303,6 +333,8 @@ static int filefrag_fibmap(int fd, int blk_shift, int *num_extents,
>> 	memset(&fm_ext, 0, sizeof(fm_ext));
>> 	memset(&fm_last, 0, sizeof(fm_last));
>> 	if (force_extent) {
>> +		memset(&fm_ext, 0, sizeof(fm_ext));
>> +		fm_ext.fe_device = st->st_dev;
>> 		fm_ext.fe_flags = FIEMAP_EXTENT_MERGED;
>> 	}
>> 
>> @@ -437,6 +469,13 @@ static int frag_report(const char *filename)
>> 			is_ext2 = 1;
>> 	}
>> 
>> +	/* Check if filesystem is Lustre.  Always print in extent format
>> +	 * with 1kB blocks, using the device-relative logical offsets. */
>> +	if (fsinfo.f_type == LUSTRE_SUPER_MAGIC) {
>> +		device_offset = 1;
>> +		blocksize = blocksize ?: 1024;
>> +	}
>> +
>> 	if (is_ext2) {
>> 		long cylgroups = div_ceil(fsinfo.f_blocks, blksize * 8);
>> 
>> @@ -524,10 +563,11 @@ int main(int argc, char**argv)
>> 	char **cpp;
>> 	int rc = 0, c;
>> 
>> -	while ((c = getopt(argc, argv, "Bb::eksvxX")) != EOF) {
>> +	while ((c = getopt(argc, argv, "Bb::eklsvxX")) != EOF) {
>> 		switch (c) {
>> 		case 'B':
>> 			force_bmap++;
>> +			force_extent = 0;
>> 			break;
>> 		case 'b':
>> 			if (optarg) {
>> @@ -567,6 +607,9 @@ int main(int argc, char**argv)
>> 		case 'k':
>> 			blocksize = 1024;
>> 			break;
>> +		case 'l':
>> +			device_offset++;
>> +			break;
>> 		case 's':
>> 			sync_file++;
>> 			break;
>> --
>> 2.14.3
>> 


Cheers, Andreas






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