linux-ext4 - [PATCH] ext4: add fallocate mode blocking for debugging purposes

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Date:	Sun, 13 Apr 2014 16:21:58 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc:	Namjae Jeon <linkinjeon@...il.com>, Theodore Ts'o <tytso@....edu>
Subject: [PATCH] ext4: add fallocate mode blocking for debugging purposes

If a particular fallocate mode is causing test failures, give the
tester the ability to block a particular fallocate mode so that the
use of a particular fallocate mode will be reported as not supported.

For example, if the COLLAPSE_RANGE fallocate mode is causing test
failures, this allows us to suppress it so we can more easily test the
rest of the file system code.

Signed-off-by: "Theodore Ts'o" <tytso@....edu>
---
 fs/ext4/extents.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 64b4003..1bb3e4b 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -29,6 +29,7 @@
  *   - smart tree reduction
  */
 
+#include <linux/module.h>
 #include <linux/fs.h>
 #include <linux/time.h>
 #include <linux/jbd2.h>
@@ -4862,6 +4863,12 @@ out_mutex:
 	return ret;
 }
 
+int ext4_fallocate_mode_block __read_mostly;
+
+module_param_named(fallocate_mode_block, ext4_fallocate_mode_block, int, 0644);
+MODULE_PARM_DESC(fallocate_mode_block,
+		 "Fallocate modes which are blocked for debugging purposes");
+
 /*
  * preallocate space for a file. This implements ext4's fallocate file
  * operation, which gets called from sys_fallocate system call.
@@ -4881,6 +4888,13 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
 	struct timespec tv;
 	unsigned int blkbits = inode->i_blkbits;
 
+	/*
+	 * for debugging purposes, allow certain fallocate operations
+	 * to be disabled
+	 */
+	if (unlikely(mode & ext4_fallocate_mode_block))
+		return -EOPNOTSUPP;
+
 	/* Return error if mode is not supported */
 	if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE |
 		     FALLOC_FL_COLLAPSE_RANGE | FALLOC_FL_ZERO_RANGE))
-- 
1.9.0

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