[PATCH] xfs_io: Allow "open -P" to specify O_PATH

* [PATCH] xfs_io: Allow "open -P" to specify O_PATH
@ 2017-03-28 14:29 David Howells
  2017-03-29 21:52 ` [PATCH] xfs_io: Allow -P and -L to be given to open for O_PATH and O_NOFOLLOW David Howells
                   ` (2 more replies)
  0 siblings, 3 replies; 9+ messages in thread
From: David Howells @ 2017-03-28 14:29 UTC (permalink / raw)
  To: linux-xfs
  Cc: dhowells, Andreas Dilger, Christoph Hellwig, linux-fsdevel, Eric Sandeen

xfs_io: Allow "open -P" to specify O_PATH

Allow "open -P" to specify O_PATH so that paths which would otherwise be
unopenable might be opened for stat()'ing.  Such things include files that
would incur an access error or device files for which no corresponding
driver is available.

Signed-off-by: David Howells <dhowells@redhat.com>
---
 io/io.h           |    1 +
 io/open.c         |   13 ++++++++++++-
 man/man8/xfs_io.8 |    6 +++++-
 3 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/io/io.h b/io/io.h
index 952bdb8..b49a133 100644
--- a/io/io.h
+++ b/io/io.h
@@ -38,6 +38,7 @@
 #define IO_FOREIGN	(1<<7)
 #define IO_NONBLOCK	(1<<8)
 #define IO_TMPFILE	(1<<9)
+#define IO_PATH		(1<<10)
 
 /*
  * Regular file I/O control
diff --git a/io/open.c b/io/open.c
index 2ed55cf..9eba8ae 100644
--- a/io/open.c
+++ b/io/open.c
@@ -72,6 +72,8 @@ openfile(
 		oflags |= O_NONBLOCK;
 	if (flags & IO_TMPFILE)
 		oflags |= O_TMPFILE;
+	if (flags & IO_PATH)
+		oflags |= O_PATH;
 
 	fd = open(path, oflags, mode);
 	if (fd < 0) {
@@ -179,6 +181,7 @@ open_help(void)
 " -t -- open with O_TRUNC (truncate the file to zero length if it exists)\n"
 " -R -- mark the file as a realtime XFS file immediately after opening it\n"
 " -T -- open with O_TMPFILE (create a file not visible in the namespace)\n"
+" -P -- open with O_PATH (create an fd that is merely a location reference)\n"
 " Note1: usually read/write direct IO requests must be blocksize aligned;\n"
 "        some kernels, however, allow sectorsize alignment for direct IO.\n"
 " Note2: the bmap for non-regular files can be obtained provided the file\n"
@@ -203,7 +206,7 @@ open_f(
 		return 0;
 	}
 
-	while ((c = getopt(argc, argv, "FRTacdfm:nrstx")) != EOF) {
+	while ((c = getopt(argc, argv, "FPRTacdfm:nrstx")) != EOF) {
 		switch (c) {
 		case 'F':
 			/* Ignored / deprecated now, handled automatically */
@@ -244,6 +247,9 @@ open_f(
 		case 'T':
 			flags |= IO_TMPFILE;
 			break;
+		case 'P':
+			flags |= IO_PATH;
+			break;
 		default:
 			return command_usage(&open_cmd);
 		}
@@ -257,6 +263,11 @@ open_f(
 		return -1;
 	}
 
+	if ((flags & IO_PATH) && (flags & ~IO_PATH)) {
+		fprintf(stderr, _("-P is incompatible with other options\n"));
+		return -1;
+	}
+
 	fd = openfile(argv[optind], &geometry, flags, mode);
 	if (fd < 0)
 		return 0;
diff --git a/man/man8/xfs_io.8 b/man/man8/xfs_io.8
index 022f0ea..77ba760 100644
--- a/man/man8/xfs_io.8
+++ b/man/man8/xfs_io.8
@@ -122,7 +122,7 @@ command for more details on any command.
 Display a list of all open files and (optionally) switch to an alternate
 current open file.
 .TP
-.BI "open [[ \-acdfrstRT ] " path " ]"
+.BI "open [[ \-acdfrstRTP ] " path " ]"
 Closes the current file, and opens the file specified by
 .I path
 instead. Without any arguments, displays statistics about the current
@@ -164,6 +164,10 @@ option.
 .B \-R
 marks the file as a realtime XFS file after
 opening it, if it is not already marked as such.
+.TP
+.B \-P
+opens the path as a referent only (O_PATH).  This is incompatible with other
+flags specifying other O_xxx flags.
 .PD
 .RE
 .TP

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