On Wed, 2023-04-12 at 16:54 +0300, Amir Goldstein wrote:
> Introduce the format lowerdir=lower1:lower2::lowerdata1:lowerdata2
> where the lower layers after the :: separator are not merged into the
> overlayfs merge dirs.
>
> The files in those layers are only meant to be accessible via
> absolute
> redirect from metacopy files in lower layers. Following changes will
> implement lookup in the data layers.
>
> This feature was requested for composefs ostree use case, where the
> lower data layer should only be accessiable via absolute redirects
> from metacopy inodes.
>
> The lower data layers are not required to a have a unique uuid or any
> uuid at all, because they are never used to compose the overlayfs
> inode
> st_ino/st_dev.
>
> Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
Reviewed-by: Alexander Larsson <alexl@xxxxxxxxxx>
> ---
> Documentation/filesystems/overlayfs.rst | 32 +++++++++++++++++
> fs/overlayfs/namei.c | 4 +--
> fs/overlayfs/ovl_entry.h | 9 +++++
> fs/overlayfs/super.c | 46 +++++++++++++++++++++--
> --
> 4 files changed, 82 insertions(+), 9 deletions(-)
>
> diff --git a/Documentation/filesystems/overlayfs.rst
> b/Documentation/filesystems/overlayfs.rst
> index 4c76fda07645..c8e04a4f0e21 100644
> --- a/Documentation/filesystems/overlayfs.rst
> +++ b/Documentation/filesystems/overlayfs.rst
> @@ -371,6 +371,38 @@ conflict with metacopy=on, and will result in an
> error.
> [*] redirect_dir=follow only conflicts with metacopy=on if
> upperdir=... is
> given.
>
> +
> +Data-only lower layers
> +----------------------
> +
> +With "metacopy" feature enabled, an overlayfs regular file may be a
> composition
> +of information from up to three different layers:
> +
> + 1) metadata from a file in the upper layer
> +
> + 2) st_ino and st_dev object identifier from a file in a lower layer
> +
> + 3) data from a file in another lower layer (further below)
> +
> +The "lower data" file can be on any lower layer, except from the top
> most
> +lower layer.
> +
> +Below the top most lower layer, any number of lower most layers may
> be defined
> +as "data-only" lower layers, using the double collon ("::")
> separator.
"colon", not "collon"
> +
> +For example:
> +
> + mount -t overlay overlay -olowerdir=/lower1::/lower2:/lower3
> /merged
> +
> +The paths of files in the "data-only" lower layers are not visible
> in the
> +merged overlayfs directories and the metadata and st_ino/st_dev of
> files
> +in the "data-only" lower layers are not visible in overlayfs inodes.
> +
> +Only the data of the files in the "data-only" lower layers may be
> visible
> +when a "metacopy" file in one of the lower layers above it, has a
> "redirect"
> +to the absolute path of the "lower data" file in the "data-only"
> lower layer.
> +
> +
> Sharing and copying layers
> --------------------------
>
> diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
> index b629261324f1..ff82155b4f7e 100644
> --- a/fs/overlayfs/namei.c
> +++ b/fs/overlayfs/namei.c
> @@ -356,7 +356,7 @@ int ovl_check_origin_fh(struct ovl_fs *ofs,
> struct ovl_fh *fh, bool connected,
> struct dentry *origin = NULL;
> int i;
>
> - for (i = 1; i < ofs->numlayer; i++) {
> + for (i = 1; i <= ovl_numlowerlayer(ofs); i++) {
> /*
> * If lower fs uuid is not unique among lower fs we
> cannot match
> * fh->uuid to layer.
> @@ -907,7 +907,7 @@ struct dentry *ovl_lookup(struct inode *dir,
> struct dentry *dentry,
>
> if (!d.stop && ovl_numlower(poe)) {
> err = -ENOMEM;
> - stack = ovl_stack_alloc(ofs->numlayer - 1);
> + stack = ovl_stack_alloc(ovl_numlowerlayer(ofs));
> if (!stack)
> goto out_put_upper;
> }
Again, surely ovl_numlower(poe) is a better size here?
> diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
> index 221f0cbe748e..25fabb3175cf 100644
> --- a/fs/overlayfs/ovl_entry.h
> +++ b/fs/overlayfs/ovl_entry.h
> @@ -62,6 +62,8 @@ struct ovl_fs {
> unsigned int numlayer;
> /* Number of unique fs among layers including upper fs */
> unsigned int numfs;
> + /* Number of data-only lower layers */
> + unsigned int numdatalayer;
> const struct ovl_layer *layers;
> struct ovl_sb *fs;
> /* workbasedir is the path at workdir= mount option */
> @@ -95,6 +97,13 @@ struct ovl_fs {
> errseq_t errseq;
> };
>
> +
> +/* Number of lower layers, not including data-only layers */
> +static inline unsigned int ovl_numlowerlayer(struct ovl_fs *ofs)
> +{
> + return ofs->numlayer - ofs->numdatalayer - 1;
> +}
> +
> static inline struct vfsmount *ovl_upper_mnt(struct ovl_fs *ofs)
> {
> return ofs->layers[0].mnt;
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index 7742aef3f3b3..3484f39a8f27 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -1579,6 +1579,16 @@ static int ovl_get_fsid(struct ovl_fs *ofs,
> const struct path *path)
> return ofs->numfs++;
> }
>
> +/*
> + * The fsid after the last lower fsid is used for the data layers.
> + * It is a "null fs" with a null sb, null uuid, and no pseudo dev.
> + */
> +static int ovl_get_data_fsid(struct ovl_fs *ofs)
> +{
> + return ofs->numfs;
> +}
> +
> +
> static int ovl_get_layers(struct super_block *sb, struct ovl_fs
> *ofs,
> struct path *stack, unsigned int numlower,
> struct ovl_layer *layers)
> @@ -1586,11 +1596,14 @@ static int ovl_get_layers(struct super_block
> *sb, struct ovl_fs *ofs,
> int err;
> unsigned int i;
>
> - ofs->fs = kcalloc(numlower + 1, sizeof(struct ovl_sb),
> GFP_KERNEL);
> + ofs->fs = kcalloc(numlower + 2, sizeof(struct ovl_sb),
> GFP_KERNEL);
> if (ofs->fs == NULL)
> return -ENOMEM;
>
> - /* idx/fsid 0 are reserved for upper fs even with lower only
> overlay */
> + /*
> + * idx/fsid 0 are reserved for upper fs even with lower only
> overlay
> + * and the last fsid is reserved for "null fs" of the data
> layers.
> + */
> ofs->numfs++;
>
> /*
> @@ -1615,7 +1628,10 @@ static int ovl_get_layers(struct super_block
> *sb, struct ovl_fs *ofs,
> struct inode *trap;
> int fsid;
>
> - fsid = ovl_get_fsid(ofs, &stack[i]);
> + if (i < numlower - ofs->numdatalayer)
> + fsid = ovl_get_fsid(ofs, &stack[i]);
> + else
> + fsid = ovl_get_data_fsid(ofs);
> if (fsid < 0)
> return fsid;
>
> @@ -1703,6 +1719,7 @@ static int ovl_get_lowerstack(struct
> super_block *sb, struct ovl_entry *oe,
> int err;
> struct path *stack = NULL;
> struct ovl_path *lowerstack;
> + unsigned int numlowerdata = 0;
> unsigned int i;
>
> if (!ofs->config.upperdir && numlower == 1) {
> @@ -1714,13 +1731,27 @@ static int ovl_get_lowerstack(struct
> super_block *sb, struct ovl_entry *oe,
> if (!stack)
> return -ENOMEM;
>
> - err = -EINVAL;
> - for (i = 0; i < numlower; i++) {
> + for (i = 0; i < numlower;) {
> err = ovl_lower_dir(lower, &stack[i], ofs, &sb-
> >s_stack_depth);
> if (err)
> goto out_err;
>
> lower = strchr(lower, '\0') + 1;
> +
> + i++;
> + err = -EINVAL;
> + /* :: seperator indicates the start of lower data
> layers */
> + if (!*lower && i < numlower && !numlowerdata) {
> + if (!ofs->config.metacopy) {
> + pr_err("lower data-only dirs require
> metacopy support.\n");
> + goto out_err;
> + }
> + lower++;
> + numlower--;
> + ofs->numdatalayer = numlowerdata = numlower -
> i;
> + pr_info("using the lowest %d of %d lowerdirs
> as data layers\n",
> + numlowerdata, numlower);
> + }
> }
This will handle a "::" at the end of the string as an error. Maybe it
would be better to treat it as "zero lower data layera", to make code
that generates mount options more regular? Not a huge issue though.
> err = -EINVAL;
> @@ -1734,12 +1765,13 @@ static int ovl_get_lowerstack(struct
> super_block *sb, struct ovl_entry *oe,
> if (err)
> goto out_err;
>
> - err = ovl_init_entry(oe, NULL, numlower);
> + /* Data-only layers are not merged in root directory */
> + err = ovl_init_entry(oe, NULL, numlower - numlowerdata);
> if (err)
> goto out_err;
>
> lowerstack = ovl_lowerstack(oe);
> - for (i = 0; i < numlower; i++) {
> + for (i = 0; i < numlower - numlowerdata; i++) {
> lowerstack[i].dentry = dget(stack[i].dentry);
> lowerstack[i].layer = &ofs->layers[i+1];
> }
--
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
=-=-=
Alexander Larsson Red Hat,
Inc
alexl@xxxxxxxxxx alexander.larsson@xxxxxxxxx
He's a one-legged native American master criminal on the edge. She's a
supernatural paranoid wrestler with someone else's memories. They fight
crime!
