linux-ext4 - RE: libext2fs: don't flush to device opened in read-only mode

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Message-ID: <118AAB5F26BFB34DB5CDA7DA33334DB9B6072B@vmsk-exch-01.paragon-software.com>
Date:   Thu, 25 May 2017 12:12:21 +0000
From:   Konstantin Chistyakov <Konstantin.Chistyakov@...agon-software.com>
To:     Theodore Ts'o <tytso@....edu>
CC:     "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: RE: libext2fs: don't flush to device opened in read-only mode

Updating path:
Subject: [PATCH] e2fsck: don't flush to device opened in read-only mode

If the e2fsck is called with both -f -n options, the checking completing with a flushing error (retcode 8).
e2fsprogs 1.43.4, builded in CygWin (cygwin1.dll 2.8.0 x64), Windows 8.1 x64 and Windows 10 x64 (not tested on x86).
In path added read-only test for flushing block in 'e2fsck/unix.c';

Catch error from the ext2fs_flush(ctx->fs)  when ctx->fs is opened in read-only mode:

...
e2fsck -n -f /dev/sdd1
e2fsck 1.43.4 (31-Jan-2017)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
Error flushing writes to storage device: Permission denied

---
(limited to 'e2fsck/unix.c')

diff --git a/e2fsck/unix.c b/e2fsck/unix.c
index b602553..ff96148 100644
--- a/e2fsck/unix.c
+++ b/e2fsck/unix.c
@@ -1898,15 +1898,17 @@ no_journal:
 		ext2fs_mark_super_dirty(fs);
 	}
 
-	e2fsck_write_bitmaps(ctx);
-	if (fs->flags & EXT2_FLAG_DIRTY) {
-		pctx.errcode = ext2fs_flush(ctx->fs);
+	if (!(ctx->options & E2F_OPT_READONLY)) {
+		e2fsck_write_bitmaps(ctx);
+		if (fs->flags & EXT2_FLAG_DIRTY) {
+			pctx.errcode = ext2fs_flush(ctx->fs);
+			if (pctx.errcode)
+				fix_problem(ctx, PR_6_FLUSH_FILESYSTEM, &pctx);
+		}
+		pctx.errcode = io_channel_flush(ctx->fs->io);
 		if (pctx.errcode)
-			fix_problem(ctx, PR_6_FLUSH_FILESYSTEM, &pctx);
+			fix_problem(ctx, PR_6_IO_FLUSH, &pctx);
 	}
-	pctx.errcode = io_channel_flush(ctx->fs->io);
-	if (pctx.errcode)
-		fix_problem(ctx, PR_6_IO_FLUSH, &pctx);
 
 	if (was_changed) {
 		int fs_fixed = (ctx->flags & E2F_FLAG_PROBLEMS_FIXED);

-----Original Message-----
From: Konstantin Chistyakov 
Sent: Thursday, May 25, 2017 8:50 AM
To: 'Theodore Ts'o' <tytso@....edu>
Cc: 'linux-ext4@...r.kernel.org' <linux-ext4@...r.kernel.org>
Subject: RE: libext2fs: don't flush to device opened in read-only mode

Thanks for suggestion how to fix the bug correctly. Platform for reproducing: CYGWin build (x86, x64, cygwin1.dll v.2.8.0), Windows 8.1 x64 and Windows  10 x64 (x86 not tested).

-----Original Message-----
From: Theodore Ts'o [mailto:tytso@....edu]
Sent: Thursday, May 25, 2017 12:56 AM
To: Konstantin Chistyakov <Konstantin.Chistyakov@...agon-software.com>
Cc: linux-ext4@...r.kernel.org
Subject: Re: libext2fs: don't flush to device opened in read-only mode

On Mon, May 22, 2017 at 09:48:00AM +0000, Konstantin Chistyakov wrote:
> From: Konstantin Chistyakov
> <Konstantin.Chistyakov@...agon-software.com>
> Date: Tue, 19 May 2017 09:23:29 -0600
> Subject: [PATCH] libext2fs: don't flush to device opened in read-only 
> mode
> 
> From: Konstantin Chistyakov
> <Konstantin.Chistyakov@...agon-software.com>
> 
> If the e2fsck is called with both -f -n options, the checking completing with a flushing error (retcode 8).
> 
> Catch error from the unix_flush() fsync(data->dev) when data->dev is opened in read-only mode:

I can't reproduce this problem.  What storage device or operating system are you using?

That being said, this is probably the wrong place to fix it.  The better fix is in e2fsck/unix.c, by adding a read-only test.

       	      	 		   	  - Ted