From: Hao Luo <haoluo@google.com>
To: Amir Goldstein <amir73il@gmail.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>
Subject: Re: Overlayfs with writable lower layer
Date: Tue, 13 Sep 2022 13:33:42 -0700 [thread overview]
Message-ID: <CA+khW7h907VDeD1mR2wH4pOWxPBG18C2enkZKSZgyWYrFP7Vnw@mail.gmail.com> (raw)
In-Reply-To: <CAOQ4uxjP0qeuUrdjT6hXCb5zO0AoY+LKM6uza2cL9UCGMo8KsQ@mail.gmail.com>
On Tue, Sep 13, 2022 at 11:54 AM Amir Goldstein <amir73il@gmail.com> wrote:
> OK. IIUC, you have upper fs files only in the root dir?
Sorry, no, the upper fs files need to be in subdir.
> And the lower root dir has only subdirs?
There could be files.
> Can you give a small example of an upper a lower and their
> union trees just for the sake of discussion?
>
For example, assume lower has the following layout:
$ tree lower
.
└── A
├── B
│ └── lower
└── lower
I can't create files in the fs in the lower.
$ touch A/B/file
touch: cannot touch 'A/B/file': Permission denied
The upper is initially empty.
I would like to overlay a writable fs on top of lower, so the union
tree looks like
$ tree union
.
└── A
├── B
│ └── lower
└── lower
$ touch A/B/file
$ tree union
.
└── A
├── B
│ ├── file
│ └── lower2
└── lower1
Here, 'file' exists in the upper.
Further, directory B could disappear from lower. When that happens, I
think there are two possible behaviors:
- make 'file' disappear from union as well;
- make 'file' and its directory accessible as well.
In behavior 1, it will look like
$ tree union
.
└── A
└── lower1
In behavior 2, it will look like
$ tree union
.
└── A
├── B
│ └── file
└── lower1
IMHO, behavior 1 works better in my use case. But if the FS experts
think behavior 2 makes more sense, I can work around.
>
> If that is all then it sounds pretty simple.
> It could be described something like this:
> 1. merged directories cannot appear/disappear
> 2. lower pure directories can appear/disappear
> 3. upper files/dirs can be created inside merge dirs and pure upper dirs
>
> I think I have some patches that could help with #2.
>
These three semantics looks good to me.
> Thanks,
> Amir.
next prev parent reply other threads:[~2022-09-13 20:33 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-25 15:30 [PATCH RESEND V12 0/8] fuse: Add support for passthrough read/write Alessio Balsini
2021-01-25 15:30 ` [PATCH RESEND V12 1/8] fs: Generic function to convert iocb to rw flags Alessio Balsini
2021-01-25 16:46 ` Alessio Balsini
2021-03-24 7:43 ` Rokudo Yan
2021-03-24 14:02 ` Alessio Balsini
2021-01-25 15:30 ` [PATCH RESEND V12 2/8] fuse: 32-bit user space ioctl compat for fuse device Alessio Balsini
[not found] ` <CAMAHBGzkfEd9-1u0iKXp65ReJQgUi_=4sMpmfkwEOaMp6Ux7pg@mail.gmail.com>
2021-01-27 13:40 ` Alessio Balsini
[not found] ` <CAMAHBGwpKW+30kNQ_Apt8A-FTmr94hBOzkT21cjEHHW+t7yUMQ@mail.gmail.com>
2021-01-28 14:15 ` Alessio Balsini
2021-02-05 9:54 ` Peng Tao
2021-03-16 18:57 ` Arnd Bergmann
2021-02-17 10:21 ` Miklos Szeredi
2021-03-01 12:26 ` Alessio Balsini
2021-03-16 18:53 ` Arnd Bergmann
2021-03-18 16:13 ` Alessio Balsini
2021-03-18 21:15 ` Arnd Bergmann
2021-03-19 15:21 ` Alessio Balsini
2021-01-25 15:30 ` [PATCH RESEND V12 3/8] fuse: Definitions and ioctl for passthrough Alessio Balsini
2021-02-17 13:41 ` Miklos Szeredi
2021-02-19 7:05 ` Peng Tao
2021-02-19 8:40 ` Miklos Szeredi
2021-03-01 17:05 ` Alessio Balsini
2022-09-08 15:36 ` Amir Goldstein
2022-09-09 19:07 ` Miklos Szeredi
2022-09-10 8:52 ` Amir Goldstein
2022-09-10 13:03 ` Bernd Schubert
2022-09-12 9:29 ` Miklos Szeredi
2022-09-12 12:29 ` Amir Goldstein
2022-09-12 13:03 ` Miklos Szeredi
2022-09-12 13:05 ` Miklos Szeredi
2022-09-12 13:26 ` Amir Goldstein
2022-09-12 14:22 ` Miklos Szeredi
2022-09-12 15:39 ` Amir Goldstein
2022-09-12 17:43 ` Hao Luo
2022-09-12 18:28 ` Overlayfs with writable lower layer Amir Goldstein
2022-09-13 18:26 ` Hao Luo
2022-09-13 18:54 ` Amir Goldstein
2022-09-13 20:33 ` Hao Luo [this message]
2022-09-14 3:46 ` Amir Goldstein
2022-09-14 18:00 ` Hao Luo
2022-09-14 19:23 ` Amir Goldstein
2022-09-14 19:33 ` Hao Luo
2022-09-15 10:54 ` Amir Goldstein
2023-05-12 19:37 ` [PATCH RESEND V12 3/8] fuse: Definitions and ioctl for passthrough Amir Goldstein
2023-05-15 7:29 ` Miklos Szeredi
2023-05-15 14:00 ` Amir Goldstein
2023-05-15 20:16 ` [fuse-devel] " Nikolaus Rath
2023-05-15 21:11 ` Bernd Schubert
2023-05-15 21:45 ` Paul Lawrence
2023-05-16 8:43 ` Miklos Szeredi
2023-05-16 10:16 ` Nikolaus Rath
2023-05-16 8:48 ` Amir Goldstein
2021-01-25 15:30 ` [PATCH RESEND V12 4/8] fuse: Passthrough initialization and release Alessio Balsini
2021-02-17 13:52 ` Miklos Szeredi
2021-05-05 12:21 ` Amir Goldstein
2021-05-17 11:36 ` Alessio Balsini
2021-05-17 13:21 ` Amir Goldstein
2021-01-25 15:30 ` [PATCH RESEND V12 5/8] fuse: Introduce synchronous read and write for passthrough Alessio Balsini
2021-02-17 14:00 ` Miklos Szeredi
2021-01-25 15:30 ` [PATCH RESEND V12 6/8] fuse: Handle asynchronous read and write in passthrough Alessio Balsini
2021-01-25 15:30 ` [PATCH RESEND V12 7/8] fuse: Use daemon creds in passthrough mode Alessio Balsini
2021-02-05 9:23 ` Peng Tao
2021-02-05 11:21 ` Alessio Balsini
2021-01-25 15:30 ` [PATCH RESEND V12 8/8] fuse: Introduce passthrough for mmap Alessio Balsini
2021-02-17 14:05 ` Miklos Szeredi
2021-04-01 11:24 ` Alessio Balsini
2021-11-18 18:31 ` [PATCH RESEND V12 0/8] fuse: Add support for passthrough read/write Amir Goldstein
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