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Red Hat Developers Announce Work On New "Composefs" File-System

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  • Red Hat Developers Announce Work On New "Composefs" File-System

    Phoronix: Red Hat Developers Announce Work On New "Composefs" File-System

    Red Hat engineers this morning for the first time publicly announced their work on Composefs, a new opportunistically-sharing and verified image file-system...

    https://www.phoronix.com/news/Composefs

  • #2
    why not just use erofs? NIH syndrome?

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    • #3
      Originally posted by arun54321 View Post
      why not just use erofs? NIH syndrome?
      Does it allow sharing between mounts?
      I'm actually surprised regular OverlayFS (IIUC the article) doesn't. I mean, it's common sense, the shared layers should share page cache. I assumed that was already how it worked. Or is it about file granularity sharing for intersecting-but-not-same images? Isn't the idea for those to build on top of each other without duplicating files?

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      • #4
        Originally posted by sinepgib View Post

        Does it allow sharing between mounts?
        I'm actually surprised regular OverlayFS (IIUC the article) doesn't. I mean, it's common sense, the shared layers should share page cache. I assumed that was already how it worked. Or is it about file granularity sharing for intersecting-but-not-same images? Isn't the idea for those to build on top of each other without duplicating files?
        As far as I understand, it's about sharing with intersecting images. But I don't quite understand what composefs gives you over read-only overlayfs here.

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        • #5
          Originally posted by arun54321 View Post
          why not just use erofs? NIH syndrome?
          Actually someone asked me, and my answer was why not consider finer sharing chunk-based blobs rather than file-based OSTree-like blobs. I just asked him to ask the community about this path first but soon they insisted on reinventing this :-)

          Originally posted by sinepgib View Post

          Does it allow sharing between mounts?
          Yes, see: https://www.phoronix.com/news/Linux-6.1-EROFS
          Last edited by hsiangkao; 28 November 2022, 10:17 PM.

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          • #6
            Originally posted by arun54321 View Post
            why not just use erofs? NIH syndrome?
            I believe they do very different things

            composefs isn't a physical file system, it doesn't change how data is stored on disk and uses a backing filesystem (e.g. XFS, btrfs etc). It's basically a way to say get these files, put them here and there, without copying them, mark them read-only with these properties and have a verifiable signature when loading them.

            It's basically for OStree and means it no longer needs to build a bazillion hard links that are susceptible to modification if you mount the directory as rw. It's also useful in containers since the container root filesystem can be a compiled composefs image and use a git-like object store for deduplication in user space.

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            • #7
              Originally posted by Britoid View Post

              composefs isn't a physical file system, it doesn't change how data is stored on disk and uses a backing filesystem (e.g. XFS, btrfs etc). It's basically a way to say get these files, put them here and there, without copying them, mark them read-only with these properties and have a verifiable signature when loading them.
              EROFS can get a lot blobs from backing-fses with new fscache feature as well, but in the form of chunk-based sharing, which means one blob can have a part of a file _or_ an entire file (just like what OSTree now does) _or_ several files. I wonder why OSTree per-file sharing is an effective model after introducing a filesystem with some actual metadata since we can do finer chunk-based sharing with a brand new filesystem (actually that is what composefs does as well) rather than insist on hardlink-like per-file sharing as OSTree
              Last edited by hsiangkao; 28 November 2022, 10:16 PM.

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              • #8
                So eventually at Team Red someone realized that Snap made by Team Orange was somehow good but just made poorly...

                We should invent a slogan for Linux...

                Linux where everyday something magical happens...

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                • #9
                  Originally posted by Danielsan View Post
                  So eventually at Team Red someone realized that Snap made by Team Orange was somehow good but just made poorly...

                  We should invent a slogan for Linux...

                  This is way more similar to how Flatpak does things than Snap.

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                  • #10
                    So first Stratis and now Composefs? I know they are different but still, two filesystems in development by the same company seems like a bit much to me.

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