Re: [PATCH RESEND net 3/7] net: hns3: Resolved the issue that the debugfs query result is inconsistent.

On Wed, 13 Nov 2024 13:59:32 +0800 Jijie Shao wrote:

inconsistent：
Before this modification,
if the previous read operation is stopped before complete, the buffer is not released.
In the next read operation (perhaps after a long time), the driver does not read again.
Instead, the driver returns the bufffer content, which causes outdated data to be obtained.
As a result, the obtained data is inconsistent with the actual data.

I think the word "stale" would fit the situation better.

In this patch, ppos is used to determine whether a new read operation is performed.
If yes, the driver updates the data in the buffer to ensure that the queried data is fresh.
But, if two processes read the same file at once, The read operation that ends first releases the buffer.
As a result, the other read operation re-alloc buffer memory. However, because the value of ppos is not 0,
the data is not updated again. As a result, the queried data is truncated.

This is a bug and I will fix it in the next version.

Let's say two reads are necessary to read the data:

 reader A                  reader B
  read()
   - alloc
   - hns3_dbg_read_cmd()
                           read()
                           read()
                           read(EOF) 
                            - free
  read()
   - alloc
   - hns3_dbg_read_cmd()
  read(EOF) 
   - free

The data for read A is half from one hns3_dbg_read_cmd() and half from
another. Does it not cause any actual inconsistency?

Also, just to be sure, it's not possible to lseek on these files, right?