ext4: remove timebomb in ext4_decode_extra_time()

Message ID 20170614112238.14121-1-hch@lst.de
State Superseded
Headers show

Commit Message

Christoph Hellwig June 14, 2017, 11:22 a.m.
Changing behavior based on the version code is a timebomb waiting to
happen, and not easily bisectable.  Drop it and leave any removal
to explicit developer action. (And I don't think file system
should _ever_ remove backwards compatibility that has no explicit
flag, but I'll leave that to the ext4 folks).

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/ext4/ext4.h | 12 +++---------
 1 file changed, 3 insertions(+), 9 deletions(-)

Comments

Christoph Hellwig June 27, 2017, 2:03 p.m. | #1
ping?

On Wed, Jun 14, 2017 at 01:22:38PM +0200, Christoph Hellwig wrote:
> Changing behavior based on the version code is a timebomb waiting to
> happen, and not easily bisectable.  Drop it and leave any removal
> to explicit developer action. (And I don't think file system
> should _ever_ remove backwards compatibility that has no explicit
> flag, but I'll leave that to the ext4 folks).
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/ext4/ext4.h | 12 +++---------
>  1 file changed, 3 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 32191548abed..d35749e7cf9f 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -838,21 +838,15 @@ static inline void ext4_decode_extra_time(struct timespec *time, __le32 extra)
>  {
>  	if (unlikely(sizeof(time->tv_sec) > 4 &&
>  			(extra & cpu_to_le32(EXT4_EPOCH_MASK)))) {
> -#if LINUX_VERSION_CODE < KERNEL_VERSION(4,20,0)
> +
>  		/* Handle legacy encoding of pre-1970 dates with epoch
> -		 * bits 1,1.  We assume that by kernel version 4.20,
> -		 * everyone will have run fsck over the affected
> -		 * filesystems to correct the problem.  (This
> -		 * backwards compatibility may be removed before this
> -		 * time, at the discretion of the ext4 developers.)
> +		 * bits 1,1. (This backwards compatibility may be removed
> +		 * at the discretion of the ext4 developers.)
>  		 */
>  		u64 extra_bits = le32_to_cpu(extra) & EXT4_EPOCH_MASK;
>  		if (extra_bits == 3 && ((time->tv_sec) & 0x80000000) != 0)
>  			extra_bits = 0;
>  		time->tv_sec += extra_bits << 32;
> -#else
> -		time->tv_sec += (u64)(le32_to_cpu(extra) & EXT4_EPOCH_MASK) << 32;
> -#endif
>  	}
>  	time->tv_nsec = (le32_to_cpu(extra) & EXT4_NSEC_MASK) >> EXT4_EPOCH_BITS;
>  }
> -- 
> 2.11.0
---end quoted text---
Eric Biggers June 27, 2017, 6:35 p.m. | #2
On Tue, Jun 27, 2017 at 04:03:26PM +0200, Christoph Hellwig wrote:
> ping?
> 
> On Wed, Jun 14, 2017 at 01:22:38PM +0200, Christoph Hellwig wrote:
> > Changing behavior based on the version code is a timebomb waiting to
> > happen, and not easily bisectable.  Drop it and leave any removal
> > to explicit developer action. (And I don't think file system
> > should _ever_ remove backwards compatibility that has no explicit
> > flag, but I'll leave that to the ext4 folks).
> > 
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > ---
> >  fs/ext4/ext4.h | 12 +++---------
> >  1 file changed, 3 insertions(+), 9 deletions(-)
> > 
> > diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> > index 32191548abed..d35749e7cf9f 100644
> > --- a/fs/ext4/ext4.h
> > +++ b/fs/ext4/ext4.h
> > @@ -838,21 +838,15 @@ static inline void ext4_decode_extra_time(struct timespec *time, __le32 extra)
> >  {
> >  	if (unlikely(sizeof(time->tv_sec) > 4 &&
> >  			(extra & cpu_to_le32(EXT4_EPOCH_MASK)))) {
> > -#if LINUX_VERSION_CODE < KERNEL_VERSION(4,20,0)
> > +
> >  		/* Handle legacy encoding of pre-1970 dates with epoch
> > -		 * bits 1,1.  We assume that by kernel version 4.20,
> > -		 * everyone will have run fsck over the affected
> > -		 * filesystems to correct the problem.  (This
> > -		 * backwards compatibility may be removed before this
> > -		 * time, at the discretion of the ext4 developers.)
> > +		 * bits 1,1. (This backwards compatibility may be removed
> > +		 * at the discretion of the ext4 developers.)
> >  		 */
> >  		u64 extra_bits = le32_to_cpu(extra) & EXT4_EPOCH_MASK;
> >  		if (extra_bits == 3 && ((time->tv_sec) & 0x80000000) != 0)
> >  			extra_bits = 0;
> >  		time->tv_sec += extra_bits << 32;
> > -#else
> > -		time->tv_sec += (u64)(le32_to_cpu(extra) & EXT4_EPOCH_MASK) << 32;
> > -#endif
> >  	}
> >  	time->tv_nsec = (le32_to_cpu(extra) & EXT4_NSEC_MASK) >> EXT4_EPOCH_BITS;
> >  }

Looks good --- I agree that timebombs are a very bad idea.

Reviewed-by: Eric Biggers <ebiggers@google.com>

- Eric
Christoph Hellwig July 18, 2017, 4:18 p.m. | #3
ping^2?

On Tue, Jun 27, 2017 at 04:03:26PM +0200, Christoph Hellwig wrote:
> ping?
> 
> On Wed, Jun 14, 2017 at 01:22:38PM +0200, Christoph Hellwig wrote:
> > Changing behavior based on the version code is a timebomb waiting to
> > happen, and not easily bisectable.  Drop it and leave any removal
> > to explicit developer action. (And I don't think file system
> > should _ever_ remove backwards compatibility that has no explicit
> > flag, but I'll leave that to the ext4 folks).
> > 
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > ---
> >  fs/ext4/ext4.h | 12 +++---------
> >  1 file changed, 3 insertions(+), 9 deletions(-)
> > 
> > diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> > index 32191548abed..d35749e7cf9f 100644
> > --- a/fs/ext4/ext4.h
> > +++ b/fs/ext4/ext4.h
> > @@ -838,21 +838,15 @@ static inline void ext4_decode_extra_time(struct timespec *time, __le32 extra)
> >  {
> >  	if (unlikely(sizeof(time->tv_sec) > 4 &&
> >  			(extra & cpu_to_le32(EXT4_EPOCH_MASK)))) {
> > -#if LINUX_VERSION_CODE < KERNEL_VERSION(4,20,0)
> > +
> >  		/* Handle legacy encoding of pre-1970 dates with epoch
> > -		 * bits 1,1.  We assume that by kernel version 4.20,
> > -		 * everyone will have run fsck over the affected
> > -		 * filesystems to correct the problem.  (This
> > -		 * backwards compatibility may be removed before this
> > -		 * time, at the discretion of the ext4 developers.)
> > +		 * bits 1,1. (This backwards compatibility may be removed
> > +		 * at the discretion of the ext4 developers.)
> >  		 */
> >  		u64 extra_bits = le32_to_cpu(extra) & EXT4_EPOCH_MASK;
> >  		if (extra_bits == 3 && ((time->tv_sec) & 0x80000000) != 0)
> >  			extra_bits = 0;
> >  		time->tv_sec += extra_bits << 32;
> > -#else
> > -		time->tv_sec += (u64)(le32_to_cpu(extra) & EXT4_EPOCH_MASK) << 32;
> > -#endif
> >  	}
> >  	time->tv_nsec = (le32_to_cpu(extra) & EXT4_NSEC_MASK) >> EXT4_EPOCH_BITS;
> >  }
> > -- 
> > 2.11.0
> ---end quoted text---
---end quoted text---

Patch

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 32191548abed..d35749e7cf9f 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -838,21 +838,15 @@  static inline void ext4_decode_extra_time(struct timespec *time, __le32 extra)
 {
 	if (unlikely(sizeof(time->tv_sec) > 4 &&
 			(extra & cpu_to_le32(EXT4_EPOCH_MASK)))) {
-#if LINUX_VERSION_CODE < KERNEL_VERSION(4,20,0)
+
 		/* Handle legacy encoding of pre-1970 dates with epoch
-		 * bits 1,1.  We assume that by kernel version 4.20,
-		 * everyone will have run fsck over the affected
-		 * filesystems to correct the problem.  (This
-		 * backwards compatibility may be removed before this
-		 * time, at the discretion of the ext4 developers.)
+		 * bits 1,1. (This backwards compatibility may be removed
+		 * at the discretion of the ext4 developers.)
 		 */
 		u64 extra_bits = le32_to_cpu(extra) & EXT4_EPOCH_MASK;
 		if (extra_bits == 3 && ((time->tv_sec) & 0x80000000) != 0)
 			extra_bits = 0;
 		time->tv_sec += extra_bits << 32;
-#else
-		time->tv_sec += (u64)(le32_to_cpu(extra) & EXT4_EPOCH_MASK) << 32;
-#endif
 	}
 	time->tv_nsec = (le32_to_cpu(extra) & EXT4_NSEC_MASK) >> EXT4_EPOCH_BITS;
 }