On Mon, Feb 6, 2017 at 1:32 PM, zhangyi (F) <yi.zhang@xxxxxxxxxx> wrote:
> Hi:
> We found that we cannot read the latest data from an opened file(eg: "testfile") in overlayfs
> which was opened in read-only mode(this file was originally located in the lowerdir and
> mapped in the mergedir, and then was copied to upperdir when someone added some data later).
>
> For example:
>
> lower: testfile(empty)
> upper: empty
> work: empty
> merge: empty
>
> mount -t overlay -o lowerdir=lower,upperdir=upper,workdir=work overlayfs merge
>
> 1) fd1 = open("merge/testfile", O_RDONLY);
> 2) fd2 = open("merge/testfile", O_WRONLY | O_APPEND);
> then we write some new data to fd2.
> 3) read data form fd1.
>
> expect results: we read data which was written used by fd2.
> reality results: nothing.
>
> We cannot read data from the copied file in the upperdir use fd1, so do we need to fix it?
This is a documented quirk (see section "Non-standard behavior" in
Documentation/filesystems/overlayfs.txt).
Hopefully will have a fix in a future version.
Thanks,
Miklos
>
> Thanks,
> zhangyi
>
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