On Fri, Oct 6, 2017 at 8:47 PM, 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 metadata copyup is conditional on index=on. If index=off and user
> specifies metacopy=on, it goes back to metacopy=off and a warning is
> printed.
>
> Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
> ---
> fs/overlayfs/Kconfig | 9 +++++++++
> fs/overlayfs/ovl_entry.h | 1 +
> fs/overlayfs/super.c | 32 ++++++++++++++++++++++++++++++++
> 3 files changed, 42 insertions(+)
>
> diff --git a/fs/overlayfs/Kconfig b/fs/overlayfs/Kconfig
> index cbfc196e5dc5..94d4c61719c8 100644
> --- a/fs/overlayfs/Kconfig
> +++ b/fs/overlayfs/Kconfig
> @@ -43,3 +43,12 @@ 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
> + depends on OVERLAY_FS_INDEX
> + 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 878a750986dd..a49f61111c79 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;
> };
>
> /* private information held for overlayfs's superblock */
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index fd5ea4facc62..338fb0c3d345 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -39,6 +39,11 @@ module_param_named(index, ovl_index_def, bool, 0644);
> MODULE_PARM_DESC(ovl_index_def,
> "Default to on or off for the inodes index feature");
>
> +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;
> @@ -302,6 +307,9 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
> if (ufs->config.index != ovl_index_def)
> seq_printf(m, ",index=%s",
> ufs->config.index ? "on" : "off");
> + if (ufs->config.metacopy != ovl_metacopy_def)
> + seq_printf(m, ",metacopy=%s",
> + ufs->config.metacopy ? "on" : "off");
> return 0;
> }
>
> @@ -335,6 +343,8 @@ enum {
> OPT_REDIRECT_DIR_OFF,
> OPT_INDEX_ON,
> OPT_INDEX_OFF,
> + OPT_METACOPY_ON,
> + OPT_METACOPY_OFF,
> OPT_ERR,
> };
>
> @@ -347,6 +357,8 @@ 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}
> };
>
> @@ -427,6 +439,14 @@ 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;
> @@ -441,6 +461,12 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
> config->workdir = NULL;
> }
>
> + /* As of now metacopy=on is dependent on index=on */
> + if (config->metacopy && !config->index) {
> + pr_warn("overlayfs: can not enable metadata only copyup with index=off. Falling back to metacopy=off\n");
> + config->metacopy = false;
> + }
> +
There are later places in fill_super where index may be falling back to off
due to missing file handle support in lower fs.
Please move this check to much later to make sure metacopy=on and index=off
cannot co-exists.
Thanks,
Amir.
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