Re: [PATCH 03/21] fs/bdev: Add atomic write support info to statx

From: John Garry
Date: Mon Oct 02 2023 - 05:52:16 EST


On 01/10/2023 14:23, Bart Van Assche wrote:
On 9/29/23 15:49, Eric Biggers wrote:
On Fri, Sep 29, 2023 at 10:27:08AM +0000, John Garry wrote:
diff --git a/include/uapi/linux/stat.h b/include/uapi/linux/stat.h
index 7cab2c65d3d7..c99d7cac2aa6 100644
--- a/include/uapi/linux/stat.h
+++ b/include/uapi/linux/stat.h
@@ -127,7 +127,10 @@ struct statx {
      __u32    stx_dio_mem_align;    /* Memory buffer alignment for direct I/O */
      __u32    stx_dio_offset_align;    /* File offset alignment for direct I/O */
      /* 0xa0 */
-    __u64    __spare3[12];    /* Spare space for future expansion */
+    __u32    stx_atomic_write_unit_max;
+    __u32    stx_atomic_write_unit_min;

Maybe min first and then max?  That seems a bit more natural, and a lot of the
code you've written handle them in that order.

ok, I think it's fine to reorder


+#define STATX_ATTR_WRITE_ATOMIC        0x00400000 /* File supports atomic write operations */

How would this differ from stx_atomic_write_unit_min != 0?

Yeah, I suppose that we can just not set this for the case of stx_atomic_write_unit_min == 0.


Is it even possible that stx_atomic_write_unit_min == 0? My understanding
is that all Linux filesystems rely on the assumption that writing a single
logical block either succeeds or does not happen, even if a power failure
occurs between writing and reading a logical block.


Maybe they do rely on this, but is it particularly interesting?

BTW, I would not like to provide assurances that every storage media produced writes logical blocks atomically.

Thanks,
John