On 2018/6/20 5:51 PM, Arnd Bergmann wrote:
> bcache uses get_seconds() to read the current system time and store it in
> the superblock as well as in uuid_entry structures that are user visible.
>
> This changes over from the deprecated function to
> ktime_get_real_seconds(), which returns a 64-bit timestamp as it
> should. Unfortunately, the two structures are still limited to 32 bits,
> so this won't fix any real problems. Let's at least document that
> properly, in case we get an updated format in the future it can be
> fixed. Until then, we still have some time, and checking the tools
> at https://github.com/koverstreet/bcache-tools reveals no access to
> any of them.
>
> Signed-off-by: Arnd Bergmann <a...@arndb.de>
Hi Arnd,
Firstly thanks to your patch, especially the detailed information in
patch log, it helps me to understand the problem more easier.
>From the information, it seems the problem is current 32bit time stamp
will be overflow in 2106. So it will be 88 years later, which I have to
say I don't care.
Also for get_seconds() which works well for current code as many other
places call it, I would like to keep it.
But the code comments in bcache.h looks good, if you want to send a
single patch for the code comments for bcache.h, I would like to see it.
Thanks.
Coly Li
> ---
> drivers/md/bcache/super.c | 23 +++++++++++++++++------
> include/uapi/linux/bcache.h | 4 ++--
> 2 files changed, 19 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> index fa4058e43202..aa9790ee5cb5 100644
> --- a/drivers/md/bcache/super.c
> +++ b/drivers/md/bcache/super.c
> @@ -53,6 +53,17 @@ struct workqueue_struct *bcache_wq;
> /* limitation of bcache devices number on single system */
> #define BCACHE_DEVICE_IDX_MAX ((1U << MINORBITS)/BCACHE_MINORS)
>
> +/*
> + * various timestamp fields in the superblock are unfortunately
> + * limited to 32 bits, which will lead to overflow in year 2106.
> + *
> + * If we ever get a new superblock format, that should be fixed.
> + */
> +static inline u32 bcache_get_realtime32(void)
> +{
> + return (u32)ktime_get_real_seconds();
> +}
> +
> /* Superblock */
>
> static const char *read_super(struct cache_sb *sb, struct block_device *bdev,
> @@ -181,7 +192,7 @@ static const char *read_super(struct cache_sb *sb, struct
> block_device *bdev,
> goto err;
> }
>
> - sb->last_mount = get_seconds();
> + sb->last_mount = bcache_get_realtime32();
> err = NULL;
>
> get_page(bh->b_page);
> @@ -701,7 +712,7 @@ static void bcache_device_detach(struct bcache_device *d)
>
> SET_UUID_FLASH_ONLY(u, 0);
> memcpy(u->uuid, invalid_uuid, 16);
> - u->invalidated = cpu_to_le32(get_seconds());
> + u->invalidated = cpu_to_le32(bcache_get_realtime32());
> bch_uuid_write(d->c);
> }
>
> @@ -1027,7 +1038,7 @@ void bch_cached_dev_detach(struct cached_dev *dc)
> int bch_cached_dev_attach(struct cached_dev *dc, struct cache_set *c,
> uint8_t *set_uuid)
> {
> - uint32_t rtime = cpu_to_le32(get_seconds());
> + uint32_t rtime = cpu_to_le32(bcache_get_realtime32());
> struct uuid_entry *u;
> struct cached_dev *exist_dc, *t;
>
> @@ -1070,7 +1081,7 @@ int bch_cached_dev_attach(struct cached_dev *dc, struct
> cache_set *c,
> (BDEV_STATE(&dc->sb) == BDEV_STATE_STALE ||
> BDEV_STATE(&dc->sb) == BDEV_STATE_NONE)) {
> memcpy(u->uuid, invalid_uuid, 16);
> - u->invalidated = cpu_to_le32(get_seconds());
> + u->invalidated = cpu_to_le32(bcache_get_realtime32());
> u = NULL;
> }
>
> @@ -1390,7 +1401,7 @@ int bch_flash_dev_create(struct cache_set *c, uint64_t
> size)
>
> get_random_bytes(u->uuid, 16);
> memset(u->label, 0, 32);
> - u->first_reg = u->last_reg = cpu_to_le32(get_seconds());
> + u->first_reg = u->last_reg = cpu_to_le32(bcache_get_realtime32());
>
> SET_UUID_FLASH_ONLY(u, 1);
> u->sectors = size >> 9;
> @@ -1894,7 +1905,7 @@ static void run_cache_set(struct cache_set *c)
> goto err;
>
> closure_sync(&cl);
> - c->sb.last_mount = get_seconds();
> + c->sb.last_mount = bcache_get_realtime32();
> bcache_write_super(c);
>
> list_for_each_entry_safe(dc, t, &uncached_devices, list)
> diff --git a/include/uapi/linux/bcache.h b/include/uapi/linux/bcache.h
> index 821f71a2e48f..8d19e02d752a 100644
> --- a/include/uapi/linux/bcache.h
> +++ b/include/uapi/linux/bcache.h
> @@ -195,7 +195,7 @@ struct cache_sb {
> };
> };
>
> - __u32 last_mount; /* time_t */
> + __u32 last_mount; /* time overflow in y2106 */
>
> __u16 first_bucket;
> union {
> @@ -318,7 +318,7 @@ struct uuid_entry {
> struct {
> __u8 uuid[16];
> __u8 label[32];
> - __u32 first_reg;
> + __u32 first_reg; /* time overflow in y2106 */
> __u32 last_reg;
> __u32 invalidated;
>
>
