[PATCH 2/5] xfs_io: support using fallocate to map free space

From: "Darrick J. Wong" <djwong@kernel.org>
To: cem@kernel.org, djwong@kernel.org
Cc: linux-xfs@vger.kernel.org
Subject: [PATCH 2/5] xfs_io: support using fallocate to map free space
Date: Fri, 30 Dec 2022 14:20:47 -0800	[thread overview]
Message-ID: <167243884791.740087.5840342975132569721.stgit@magnolia> (raw)
In-Reply-To: <167243884763.740087.13414287212519500865.stgit@magnolia>

From: Darrick J. Wong <djwong@kernel.org>

Support FALLOC_FL_MAP_FREE_SPACE as a fallocate mode.  This is
experimental code to see if we can build a free space defragmenter out
of this.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
 io/prealloc.c     |   37 +++++++++++++++++++++++++++++++++++++
 man/man8/xfs_io.8 |    8 +++++++-
 2 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/io/prealloc.c b/io/prealloc.c
index 5805897a4a0..02de16651c1 100644
--- a/io/prealloc.c
+++ b/io/prealloc.c
@@ -32,6 +32,10 @@
 #define FALLOC_FL_UNSHARE_RANGE 0x40
 #endif
 
+#ifndef FALLOC_FL_MAP_FREE_SPACE
+#define FALLOC_FL_MAP_FREE_SPACE	(1U << 30)
+#endif
+
 static cmdinfo_t allocsp_cmd;
 static cmdinfo_t freesp_cmd;
 static cmdinfo_t resvsp_cmd;
@@ -44,6 +48,7 @@ static cmdinfo_t fcollapse_cmd;
 static cmdinfo_t finsert_cmd;
 static cmdinfo_t fzero_cmd;
 static cmdinfo_t funshare_cmd;
+static cmdinfo_t fmapfree_cmd;
 #endif
 
 static int
@@ -381,6 +386,28 @@ funshare_f(
 	}
 	return 0;
 }
+
+static int
+fmapfree_f(
+	int		argc,
+	char		**argv)
+{
+	xfs_flock64_t	segment;
+	int		mode = FALLOC_FL_MAP_FREE_SPACE;
+	int		index = 1;
+
+	if (!offset_length(argv[index], argv[index + 1], &segment)) {
+		exitcode = 1;
+		return 0;
+	}
+
+	if (fallocate(file->fd, mode, segment.l_start, segment.l_len)) {
+		perror("fallocate");
+		exitcode = 1;
+		return 0;
+	}
+	return 0;
+}
 #endif	/* HAVE_FALLOCATE */
 
 void
@@ -496,5 +523,15 @@ prealloc_init(void)
 	funshare_cmd.oneline =
 	_("unshares shared blocks within the range");
 	add_command(&funshare_cmd);
+
+	fmapfree_cmd.name = "fmapfree";
+	fmapfree_cmd.cfunc = fmapfree_f;
+	fmapfree_cmd.argmin = 2;
+	fmapfree_cmd.argmax = 2;
+	fmapfree_cmd.flags = CMD_NOMAP_OK | CMD_FOREIGN_OK;
+	fmapfree_cmd.args = _("off len");
+	fmapfree_cmd.oneline =
+	_("maps free space into a file");
+	add_command(&fmapfree_cmd);
 #endif	/* HAVE_FALLOCATE */
 }
diff --git a/man/man8/xfs_io.8 b/man/man8/xfs_io.8
index ece778fc76c..b10523325ee 100644
--- a/man/man8/xfs_io.8
+++ b/man/man8/xfs_io.8
@@ -513,8 +513,14 @@ Call fallocate with FALLOC_FL_INSERT_RANGE flag as described in the
 .BR fallocate (2)
 manual page to create the hole by shifting data blocks.
 .TP
+.BI fmapfree " offset length"
+Maps free physical space into the file by calling fallocate with
+the FALLOC_FL_MAP_FREE_SPACE flag as described in the
+.BR fallocate (2)
+manual page.
+.TP
 .BI fpunch " offset length"
-Punches (de-allocates) blocks in the file by calling fallocate with 
+Punches (de-allocates) blocks in the file by calling fallocate with
 the FALLOC_FL_PUNCH_HOLE flag as described in the
 .BR fallocate (2)
 manual page.

