xfs: teach get_bmapx about shared extents and the CoW fork

Teach xfs_getbmapx how to report shared extents and CoW fork contents
accurately in the bmap output by querying the refcount btree
appropriately.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/xfs/libxfs/xfs_fs.h

@@ -81,14 +81,16 @@ struct getbmapx {
 #define BMV_IF_PREALLOC		0x4	/* rtn status BMV_OF_PREALLOC if req */
 #define BMV_IF_DELALLOC		0x8	/* rtn status BMV_OF_DELALLOC if req */
 #define BMV_IF_NO_HOLES		0x10	/* Do not return holes */
+#define BMV_IF_COWFORK		0x20	/* return CoW fork rather than data */
 #define BMV_IF_VALID	\
 	(BMV_IF_ATTRFORK|BMV_IF_NO_DMAPI_READ|BMV_IF_PREALLOC|	\
-	 BMV_IF_DELALLOC|BMV_IF_NO_HOLES)
+	 BMV_IF_DELALLOC|BMV_IF_NO_HOLES|BMV_IF_COWFORK)
 
 /*	bmv_oflags values - returned for each non-header segment */
 #define BMV_OF_PREALLOC		0x1	/* segment = unwritten pre-allocation */
 #define BMV_OF_DELALLOC		0x2	/* segment = delayed allocation */
 #define BMV_OF_LAST		0x4	/* segment is the last in the file */
+#define BMV_OF_SHARED		0x8	/* segment shared with another file */
 
 /*
  * Structure for XFS_IOC_FSSETDM.

fs/xfs/xfs_bmap_util.c

@@ -42,6 +42,9 @@
 #include "xfs_icache.h"
 #include "xfs_log.h"
 #include "xfs_rmap_btree.h"
+#include "xfs_iomap.h"
+#include "xfs_reflink.h"
+#include "xfs_refcount.h"
 
 /* Kernel only BMAP related definitions and functions */
 
@@ -389,11 +392,13 @@ xfs_bmap_count_blocks(
 STATIC int
 xfs_getbmapx_fix_eof_hole(
 	xfs_inode_t		*ip,		/* xfs incore inode pointer */
+	int			whichfork,
 	struct getbmapx		*out,		/* output structure */
 	int			prealloced,	/* this is a file with
 						 * preallocated data space */
 	__int64_t		end,		/* last block requested */
-	xfs_fsblock_t		startblock)
+	xfs_fsblock_t		startblock,
+	bool			moretocome)
 {
 	__int64_t		fixlen;
 	xfs_mount_t		*mp;		/* file system mount point */
@@ -418,8 +423,9 @@ xfs_getbmapx_fix_eof_hole(
 		else
 			out->bmv_block = xfs_fsb_to_db(ip, startblock);
 		fileblock = XFS_BB_TO_FSB(ip->i_mount, out->bmv_offset);
-		ifp = XFS_IFORK_PTR(ip, XFS_DATA_FORK);
-		if (xfs_iext_bno_to_ext(ifp, fileblock, &lastx) &&
+		ifp = XFS_IFORK_PTR(ip, whichfork);
+		if (!moretocome &&
+		    xfs_iext_bno_to_ext(ifp, fileblock, &lastx) &&
 		   (lastx == (ifp->if_bytes / (uint)sizeof(xfs_bmbt_rec_t))-1))
 			out->bmv_oflags |= BMV_OF_LAST;
 	}
@@ -427,6 +433,81 @@ xfs_getbmapx_fix_eof_hole(
 	return 1;
 }
 
+/* Adjust the reported bmap around shared/unshared extent transitions. */
+STATIC int
+xfs_getbmap_adjust_shared(
+	struct xfs_inode		*ip,
+	int				whichfork,
+	struct xfs_bmbt_irec		*map,
+	struct getbmapx			*out,
+	struct xfs_bmbt_irec		*next_map)
+{
+	struct xfs_mount		*mp = ip->i_mount;
+	xfs_agnumber_t			agno;
+	xfs_agblock_t			agbno;
+	xfs_agblock_t			ebno;
+	xfs_extlen_t			elen;
+	xfs_extlen_t			nlen;
+	int				error;
+
+	next_map->br_startblock = NULLFSBLOCK;
+	next_map->br_startoff = NULLFILEOFF;
+	next_map->br_blockcount = 0;
+
+	/* Only written data blocks can be shared. */
+	if (!xfs_is_reflink_inode(ip) || whichfork != XFS_DATA_FORK ||
+	    map->br_startblock == DELAYSTARTBLOCK ||
+	    map->br_startblock == HOLESTARTBLOCK ||
+	    ISUNWRITTEN(map))
+		return 0;
+
+	agno = XFS_FSB_TO_AGNO(mp, map->br_startblock);
+	agbno = XFS_FSB_TO_AGBNO(mp, map->br_startblock);
+	error = xfs_reflink_find_shared(mp, agno, agbno, map->br_blockcount,
+			&ebno, &elen, true);
+	if (error)
+		return error;
+
+	if (ebno == NULLAGBLOCK) {
+		/* No shared blocks at all. */
+		return 0;
+	} else if (agbno == ebno) {
+		/*
+		 * Shared extent at (agbno, elen).  Shrink the reported
+		 * extent length and prepare to move the start of map[i]
+		 * to agbno+elen, with the aim of (re)formatting the new
+		 * map[i] the next time through the inner loop.
+		 */
+		out->bmv_length = XFS_FSB_TO_BB(mp, elen);
+		out->bmv_oflags |= BMV_OF_SHARED;
+		if (elen != map->br_blockcount) {
+			*next_map = *map;
+			next_map->br_startblock += elen;
+			next_map->br_startoff += elen;
+			next_map->br_blockcount -= elen;
+		}
+		map->br_blockcount -= elen;
+	} else {
+		/*
+		 * There's an unshared extent (agbno, ebno - agbno)
+		 * followed by shared extent at (ebno, elen).  Shrink
+		 * the reported extent length to cover only the unshared
+		 * extent and prepare to move up the start of map[i] to
+		 * ebno, with the aim of (re)formatting the new map[i]
+		 * the next time through the inner loop.
+		 */
+		*next_map = *map;
+		nlen = ebno - agbno;
+		out->bmv_length = XFS_FSB_TO_BB(mp, nlen);
+		next_map->br_startblock += nlen;
+		next_map->br_startoff += nlen;
+		next_map->br_blockcount -= nlen;
+		map->br_blockcount -= nlen;
+	}
+
+	return 0;
+}
+
 /*
  * Get inode's extents as described in bmv, and format for output.
  * Calls formatter to fill the user's buffer until all extents
@@ -459,12 +540,28 @@ xfs_getbmap(
 	int			iflags;		/* interface flags */
 	int			bmapi_flags;	/* flags for xfs_bmapi */
 	int			cur_ext = 0;
+	struct xfs_bmbt_irec	inject_map;
 
 	mp = ip->i_mount;
 	iflags = bmv->bmv_iflags;
-	whichfork = iflags & BMV_IF_ATTRFORK ? XFS_ATTR_FORK : XFS_DATA_FORK;
 
-	if (whichfork == XFS_ATTR_FORK) {
+#ifndef DEBUG
+	/* Only allow CoW fork queries if we're debugging. */
+	if (iflags & BMV_IF_COWFORK)
+		return -EINVAL;
+#endif
+	if ((iflags & BMV_IF_ATTRFORK) && (iflags & BMV_IF_COWFORK))
+		return -EINVAL;
+
+	if (iflags & BMV_IF_ATTRFORK)
+		whichfork = XFS_ATTR_FORK;
+	else if (iflags & BMV_IF_COWFORK)
+		whichfork = XFS_COW_FORK;
+	else
+		whichfork = XFS_DATA_FORK;
+
+	switch (whichfork) {
+	case XFS_ATTR_FORK:
 		if (XFS_IFORK_Q(ip)) {
 			if (ip->i_d.di_aformat != XFS_DINODE_FMT_EXTENTS &&
 			    ip->i_d.di_aformat != XFS_DINODE_FMT_BTREE &&
@@ -480,7 +577,15 @@ xfs_getbmap(
 
 		prealloced = 0;
 		fixlen = 1LL << 32;
-	} else {
+		break;
+	case XFS_COW_FORK:
+		if (ip->i_cformat != XFS_DINODE_FMT_EXTENTS)
+			return -EINVAL;
+
+		prealloced = 0;
+		fixlen = XFS_ISIZE(ip);
+		break;
+	default:
 		if (ip->i_d.di_format != XFS_DINODE_FMT_EXTENTS &&
 		    ip->i_d.di_format != XFS_DINODE_FMT_BTREE &&
 		    ip->i_d.di_format != XFS_DINODE_FMT_LOCAL)
@@ -494,6 +599,7 @@ xfs_getbmap(
 			prealloced = 0;
 			fixlen = XFS_ISIZE(ip);
 		}
+		break;
 	}
 
 	if (bmv->bmv_length == -1) {
@@ -520,7 +626,8 @@ xfs_getbmap(
 		return -ENOMEM;
 
 	xfs_ilock(ip, XFS_IOLOCK_SHARED);
-	if (whichfork == XFS_DATA_FORK) {
+	switch (whichfork) {
+	case XFS_DATA_FORK:
 		if (!(iflags & BMV_IF_DELALLOC) &&
 		    (ip->i_delayed_blks || XFS_ISIZE(ip) > ip->i_d.di_size)) {
 			error = filemap_write_and_wait(VFS_I(ip)->i_mapping);
@@ -538,8 +645,14 @@ xfs_getbmap(
 		}
 
 		lock = xfs_ilock_data_map_shared(ip);
-	} else {
+		break;
+	case XFS_COW_FORK:
+		lock = XFS_ILOCK_SHARED;
+		xfs_ilock(ip, lock);
+		break;
+	case XFS_ATTR_FORK:
 		lock = xfs_ilock_attr_map_shared(ip);
+		break;
 	}
 
 	/*
@@ -581,7 +694,8 @@ xfs_getbmap(
 			goto out_free_map;
 		ASSERT(nmap <= subnex);
 
-		for (i = 0; i < nmap && nexleft && bmv->bmv_length; i++) {
+		for (i = 0; i < nmap && nexleft && bmv->bmv_length &&
+				cur_ext < bmv->bmv_count; i++) {
 			out[cur_ext].bmv_oflags = 0;
 			if (map[i].br_state == XFS_EXT_UNWRITTEN)
 				out[cur_ext].bmv_oflags |= BMV_OF_PREALLOC;
@@ -614,9 +728,16 @@ xfs_getbmap(
 				goto out_free_map;
 			}
 
-			if (!xfs_getbmapx_fix_eof_hole(ip, &out[cur_ext],
-					prealloced, bmvend,
-					map[i].br_startblock))
+			/* Is this a shared block? */
+			error = xfs_getbmap_adjust_shared(ip, whichfork,
+					&map[i], &out[cur_ext], &inject_map);
+			if (error)
+				goto out_free_map;
+
+			if (!xfs_getbmapx_fix_eof_hole(ip, whichfork,
+					&out[cur_ext], prealloced, bmvend,
+					map[i].br_startblock,
+					inject_map.br_startblock != NULLFSBLOCK))
 				goto out_free_map;
 
 			bmv->bmv_offset =
@@ -636,11 +757,16 @@ xfs_getbmap(
 				continue;
 			}
 
+			if (inject_map.br_startblock != NULLFSBLOCK) {
+				map[i] = inject_map;
+				i--;
+			} else
 				nexleft--;
 			bmv->bmv_entries++;
 			cur_ext++;
 		}
-	} while (nmap && nexleft && bmv->bmv_length);
+	} while (nmap && nexleft && bmv->bmv_length &&
+		 cur_ext < bmv->bmv_count);
 
  out_free_map:
 	kmem_free(map);