On Fri, Nov 17, 2017 at 12:03 AM, Vivek Goyal <vgoyal@xxxxxxxxxx> wrote:
> By default metadata only copy up is disabled. Provide a mount option so
> that users can choose one way or other.
>
> Also provide a kernel config and module option to enable/disable
> metacopy feature.
>
> Like index feature, we verify on mount that upper root is not being
> reused with a different lower root. This hopes to get the configuration
> right and detect the copied layers use case. But this does only so
> much as we don't verify all the lowers. So it is possible that a lower is
> missing and later data copy up fails.
>
> Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
> ---
> fs/overlayfs/Kconfig | 8 ++++++++
> fs/overlayfs/ovl_entry.h | 1 +
> fs/overlayfs/super.c | 40 +++++++++++++++++++++++++++++++++++++---
> 3 files changed, 46 insertions(+), 3 deletions(-)
>
> diff --git a/fs/overlayfs/Kconfig b/fs/overlayfs/Kconfig
> index cbfc196e5dc5..17a0b17ad14c 100644
> --- a/fs/overlayfs/Kconfig
> +++ b/fs/overlayfs/Kconfig
> @@ -43,3 +43,11 @@ config OVERLAY_FS_INDEX
> outcomes. However, mounting the same overlay with an old kernel
> read-write and then mounting it again with a new kernel, will have
> unexpected results.
> +
> +config OVERLAY_FS_METACOPY
> + bool "Overlayfs: turn on metadata only copy up feature by default"
> + depends on OVERLAY_FS
> + help
> + If this config option is enabled then overlay filesystems will
> + copy up only metadata where appropriate and data copy up will
> + happen when a file is opended for WRITE operation.
> diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
> index 93eb6a044dd2..2720ed21ad53 100644
> --- a/fs/overlayfs/ovl_entry.h
> +++ b/fs/overlayfs/ovl_entry.h
> @@ -15,6 +15,7 @@ struct ovl_config {
> bool default_permissions;
> bool redirect_dir;
> bool index;
> + bool metacopy;
> };
>
> struct ovl_layer {
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index ee41bde87b14..d8b6b4d80d78 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -46,6 +46,11 @@ static void ovl_entry_stack_free(struct ovl_entry *oe)
> dput(oe->lowerstack[i].dentry);
> }
>
> +static bool ovl_metacopy_def = IS_ENABLED(CONFIG_OVERLAY_FS_METACOPY);
> +module_param_named(metacopy, ovl_metacopy_def, bool, 0644);
> +MODULE_PARM_DESC(ovl_metacopy_def,
> + "Default to on or off for the metadata only copy up feature");
> +
> static void ovl_dentry_release(struct dentry *dentry)
> {
> struct ovl_entry *oe = dentry->d_fsdata;
> @@ -319,6 +324,9 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
> if (ofs->config.index != ovl_index_def)
> seq_printf(m, ",index=%s",
> ofs->config.index ? "on" : "off");
> + if (ofs->config.metacopy != ovl_metacopy_def)
> + seq_printf(m, ",metacopy=%s",
> + ofs->config.metacopy ? "on" : "off");
> return 0;
> }
>
> @@ -352,6 +360,8 @@ enum {
> OPT_REDIRECT_DIR_OFF,
> OPT_INDEX_ON,
> OPT_INDEX_OFF,
> + OPT_METACOPY_ON,
> + OPT_METACOPY_OFF,
> OPT_ERR,
> };
>
> @@ -364,6 +374,8 @@ static const match_table_t ovl_tokens = {
> {OPT_REDIRECT_DIR_OFF, "redirect_dir=off"},
> {OPT_INDEX_ON, "index=on"},
> {OPT_INDEX_OFF, "index=off"},
> + {OPT_METACOPY_ON, "metacopy=on"},
> + {OPT_METACOPY_OFF, "metacopy=off"},
> {OPT_ERR, NULL}
> };
>
> @@ -444,6 +456,14 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
> config->index = false;
> break;
>
> + case OPT_METACOPY_ON:
> + config->metacopy = true;
> + break;
> +
> + case OPT_METACOPY_OFF:
> + config->metacopy = false;
> + break;
> +
> default:
> pr_err("overlayfs: unrecognized mount option \"%s\" or missing value\n", p);
> return -EINVAL;
> @@ -657,9 +677,11 @@ static int ovl_lower_dir(const char *name, struct path *path,
> * The inodes index feature needs to encode and decode file
> * handles, so it requires that all layers support them.
> */
> - if (ofs->config.index && !ovl_can_decode_fh(path->dentry->d_sb)) {
> + if ((ofs->config.index || ofs->config.metacopy) &&
> + !ovl_can_decode_fh(path->dentry->d_sb)) {
> + pr_warn("overlayfs: fs on '%s' does not support file handles, falling back to index=off and metacopy=off.\n", name);
> ofs->config.index = false;
> - pr_warn("overlayfs: fs on '%s' does not support file handles, falling back to index=off.\n", name);
> + ofs->config.metacopy = false;
> }
>
> return 0;
> @@ -923,7 +945,8 @@ static int ovl_make_workdir(struct ovl_fs *ofs, struct path *workpath)
> ofs->noxattr = true;
> ofs->config.redirect_dir = false;
> ofs->config.index = false;
> - pr_warn("overlayfs: upper fs does not support xattr, falling back to redirect_dir=off, index=off and no opaque dir.\n");
> + ofs->config.metacopy = false;
> + pr_warn("overlayfs: upper fs does not support xattr, falling back to redirect_dir=off, index=off, metacopy=off and no opaque dir.\n");
> } else {
> vfs_removexattr(ofs->workdir, OVL_XATTR_OPAQUE);
> }
> @@ -1164,6 +1187,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
>
> ofs->config.redirect_dir = ovl_redirect_dir_def;
> ofs->config.index = ovl_index_def;
> + ofs->config.metacopy = ovl_metacopy_def;
> err = ovl_parse_opt((char *) data, &ofs->config);
> if (err)
> goto out_err;
> @@ -1209,6 +1233,16 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
> else if (ofs->upper_mnt->mnt_sb != ofs->same_sb)
> ofs->same_sb = NULL;
>
> + if (!(ovl_force_readonly(ofs)) && ofs->config.metacopy) {
> + /* Verify lower root is upper root origin */
> + err = ovl_verify_origin(upperpath.dentry,
> + oe->lowerstack[0].dentry, false, true);
> + if (err) {
> + pr_err("overlayfs: failed to verify upper root origin\n");
> + goto out_free_oe;
> + }
> + }
> +
>
Fs can have upper but no workdir and you still need to verify lower
If metacopy is enabled
Amir.
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