[v3,1/5] vfs: Add file timestamp range support

Submitted by Deepa Dinamani on Feb. 18, 2017, 11:30 p.m.

Details

Message ID 1487460608-15697-2-git-send-email-deepa.kernel@gmail.com
State Superseded
Headers show

Commit Message

Deepa Dinamani Feb. 18, 2017, 11:30 p.m.
Add fields to the superblock to track the min and max
timestamps supported by filesystems.

Initially, when a superblock is allocated, initialize
it to the max and min values the fields can hold.
Individual filesystems override these to match their
actual limits.

Pseudo filesystems are assumed to always support the
min and max allowable values for the fields.

Note that the time ranges are saved in type time64_t
rather than time_t.
This is required because if we save ranges in time_t
then we would not be able to save timestamp ranges
for files that support timestamps beyond y2038.

Signed-off-by: Deepa Dinamani <deepa.kernel@gmail.com>
---
 fs/libfs.c             | 4 ++++
 fs/super.c             | 2 ++
 include/linux/fs.h     | 3 +++
 include/linux/time64.h | 2 ++
 4 files changed, 11 insertions(+)

Comments

Al Viro Feb. 19, 2017, 1:56 a.m.
On Sat, Feb 18, 2017 at 03:30:04PM -0800, Deepa Dinamani wrote:
> Add fields to the superblock to track the min and max
> timestamps supported by filesystems.
> 
> Initially, when a superblock is allocated, initialize
> it to the max and min values the fields can hold.
> Individual filesystems override these to match their
> actual limits.
> 
> Pseudo filesystems are assumed to always support the
> min and max allowable values for the fields.

> @@ -257,6 +257,8 @@ struct dentry *mount_pseudo_xattr(struct file_system_type *fs_type, char *name,
> +	s->s_time_min = TIME64_MIN;
> +	s->s_time_max = TIME64_MAX;
> @@ -518,6 +520,8 @@ int simple_fill_super(struct super_block *s, unsigned long magic,
> +	s->s_time_min = TIME64_MIN;
> +	s->s_time_max = TIME64_MAX;
> @@ -247,6 +247,8 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags,
> +	s->s_time_min = TIME64_MIN;
> +	s->s_time_max = TIME64_MAX;

If we always initialize them that way, why does libfs.c code bother
reassign the same values?
Deepa Dinamani Feb. 19, 2017, 7:23 p.m.
>> @@ -257,6 +257,8 @@ struct dentry *mount_pseudo_xattr(struct file_system_type *fs_type, char *name,
>> +     s->s_time_min = TIME64_MIN;
>> +     s->s_time_max = TIME64_MAX;
>> @@ -518,6 +520,8 @@ int simple_fill_super(struct super_block *s, unsigned long magic,
>> +     s->s_time_min = TIME64_MIN;
>> +     s->s_time_max = TIME64_MAX;
>> @@ -247,6 +247,8 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags,
>> +     s->s_time_min = TIME64_MIN;
>> +     s->s_time_max = TIME64_MAX;
>
> If we always initialize them that way, why does libfs.c code bother
> reassign the same values?

Initially, I considered the idea of having invalid range
initialization for all super blocks:
https://patchwork.kernel.org/patch/8488641/

At that point, it made sense to override the initializations in libfs.c.

The problem with this is we will have to change all filesystems at the
same time.
So I decided to change the strategy to include valid limits so that we
don't break any filesystems
and can first merge the basic infrastructure.
But, I was hoping we could go back to invalid range eventually which
is why I left the libfs.c initializations in.

But, you are right. This is redundant for now and maybe makes sense to
leave it out.
I will post an update.

Thanks,
Deepa

Patch hide | download patch | download mbox

diff --git a/fs/libfs.c b/fs/libfs.c
index 28d6f35..90ee803 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -257,6 +257,8 @@  struct dentry *mount_pseudo_xattr(struct file_system_type *fs_type, char *name,
 	s->s_op = ops ? ops : &simple_super_operations;
 	s->s_xattr = xattr;
 	s->s_time_gran = 1;
+	s->s_time_min = TIME64_MIN;
+	s->s_time_max = TIME64_MAX;
 	root = new_inode(s);
 	if (!root)
 		goto Enomem;
@@ -518,6 +520,8 @@  int simple_fill_super(struct super_block *s, unsigned long magic,
 	s->s_magic = magic;
 	s->s_op = &simple_super_operations;
 	s->s_time_gran = 1;
+	s->s_time_min = TIME64_MIN;
+	s->s_time_max = TIME64_MAX;
 
 	inode = new_inode(s);
 	if (!inode)
diff --git a/fs/super.c b/fs/super.c
index b8b6a08..f9c2241 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -247,6 +247,8 @@  static struct super_block *alloc_super(struct file_system_type *type, int flags,
 	s->s_maxbytes = MAX_NON_LFS;
 	s->s_op = &default_op;
 	s->s_time_gran = 1000000000;
+	s->s_time_min = TIME64_MIN;
+	s->s_time_max = TIME64_MAX;
 	s->cleancache_poolid = CLEANCACHE_NO_POOL;
 
 	s->s_shrink.seeks = DEFAULT_SEEKS;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index de8ed0b..ef55dfb 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1337,6 +1337,9 @@  struct super_block {
 	/* Granularity of c/m/atime in ns.
 	   Cannot be worse than a second */
 	u32		   s_time_gran;
+	/* Time limits for c/m/atime in seconds. */
+	time64_t           s_time_min;
+	time64_t           s_time_max;
 
 	/*
 	 * The next field is for VFS *only*. No filesystems have any business
diff --git a/include/linux/time64.h b/include/linux/time64.h
index 980c71b..25433b18 100644
--- a/include/linux/time64.h
+++ b/include/linux/time64.h
@@ -38,6 +38,8 @@  struct itimerspec64 {
 
 /* Located here for timespec[64]_valid_strict */
 #define TIME64_MAX			((s64)~((u64)1 << 63))
+#define TIME64_MIN			(-TIME64_MAX - 1)
+
 #define KTIME_MAX			((s64)~((u64)1 << 63))
 #define KTIME_SEC_MAX			(KTIME_MAX / NSEC_PER_SEC)