[PATCH v5 0/1] ceph: add sysfs entries signifying new mount syntax support

[PATCH v5 0/1] ceph: add sysfs entries signifying new mount syntax support

[Venky Shankar]

v5:
  - switch to sysfs instead of debugfs

[This is based on top of new mount syntax series]

Patrick/Ilya proposed the idea of having sysfs entries to signify if
kernel supports the new (v2) mount syntax. The primary use of this
information is to catch any bugs in the new syntax implementation.

This would be done as follows::

The userspace mount helper tries to mount using the new mount syntax
and fallsback to using old syntax if the mount using new syntax fails.
However, a bug in the new mount syntax implementation can silently
result in the mount helper switching to old syntax.

So, the sysfs entries can be relied upon by the mount helper to
check if the kernel supports the new mount syntax. Cases when the
mount using the new syntax fails, but the kernel does support the
new mount syntax, the mount helper could probably log before switching
to the old syntax (or fail the mount altogether when run in test mode).

sysfs entries are as follows::

    /sys/module/ceph/parameters/
    ....
    ....
    /sys/module/ceph/parameters/mount_syntax_v2
    /sys/module/ceph/parameters/mount_syntax_v1
    ....
    ....

Venky Shankar (1):
  ceph: mount syntax module parameter

 fs/ceph/super.c | 8 ++++++++
 1 file changed, 8 insertions(+)

-- 
2.27.0

[PATCH v5 1/1] ceph: mount syntax module parameter

[Venky Shankar]

Add read-only paramaters for supported mount syntaxes. Primary
user is the user-space mount helper for catching v2 syntax bugs
during testing by cross verifying if the kernel supports v2 syntax
on mount failure.

Signed-off-by: Venky Shankar <vshankar@redhat.com>
---
 fs/ceph/super.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/ceph/super.c b/fs/ceph/super.c
index 609ffc8c2d78..32e5240e33a0 100644
--- a/fs/ceph/super.c
+++ b/fs/ceph/super.c
@@ -1452,6 +1452,14 @@ bool disable_send_metrics = false;
 module_param_cb(disable_send_metrics, &param_ops_metrics, &disable_send_metrics, 0644);
 MODULE_PARM_DESC(disable_send_metrics, "Enable sending perf metrics to ceph cluster (default: on)");
 
+/* for both v1 and v2 syntax */
+bool mount_support = true;
+static const struct kernel_param_ops param_ops_mount_syntax = {
+	.get = param_get_bool,
+};
+module_param_cb(mount_syntax_v1, &param_ops_mount_syntax, &mount_support, 0444);
+module_param_cb(mount_syntax_v2, &param_ops_mount_syntax, &mount_support, 0444);
+
 module_init(init_ceph);
 module_exit(exit_ceph);
 
-- 
2.27.0

Re: [PATCH v5 1/1] ceph: mount syntax module parameter

[Jeff Layton]

On Wed, 2021-11-03 at 10:30 +0530, Venky Shankar wrote:
> Add read-only paramaters for supported mount syntaxes. Primary
> user is the user-space mount helper for catching v2 syntax bugs
> during testing by cross verifying if the kernel supports v2 syntax
> on mount failure.
> 
> Signed-off-by: Venky Shankar <vshankar@redhat.com>
> ---
>  fs/ceph/super.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/fs/ceph/super.c b/fs/ceph/super.c
> index 609ffc8c2d78..32e5240e33a0 100644
> --- a/fs/ceph/super.c
> +++ b/fs/ceph/super.c
> @@ -1452,6 +1452,14 @@ bool disable_send_metrics = false;
>  module_param_cb(disable_send_metrics, &param_ops_metrics, &disable_send_metrics, 0644);
>  MODULE_PARM_DESC(disable_send_metrics, "Enable sending perf metrics to ceph cluster (default: on)");
>  
> +/* for both v1 and v2 syntax */
> +bool mount_support = true;
> +static const struct kernel_param_ops param_ops_mount_syntax = {
> +	.get = param_get_bool,
> +};
> +module_param_cb(mount_syntax_v1, &param_ops_mount_syntax, &mount_support, 0444);
> +module_param_cb(mount_syntax_v2, &param_ops_mount_syntax, &mount_support, 0444);
> +
>  module_init(init_ceph);
>  module_exit(exit_ceph);
>  

Thanks Venky. This looks good. Merged into testing.

Note that these new parameters are not visible via modinfo, but they do
show up in /sys/module/ceph/parameters.
-- 
Jeff Layton <jlayton@redhat.com>

Re: [PATCH v5 1/1] ceph: mount syntax module parameter

[Jeff Layton]

On Wed, 2021-11-03 at 10:30 +0530, Venky Shankar wrote:
> Add read-only paramaters for supported mount syntaxes. Primary
> user is the user-space mount helper for catching v2 syntax bugs
> during testing by cross verifying if the kernel supports v2 syntax
> on mount failure.
> 
> Signed-off-by: Venky Shankar <vshankar@redhat.com>
> ---
>  fs/ceph/super.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/fs/ceph/super.c b/fs/ceph/super.c
> index 609ffc8c2d78..32e5240e33a0 100644
> --- a/fs/ceph/super.c
> +++ b/fs/ceph/super.c
> @@ -1452,6 +1452,14 @@ bool disable_send_metrics = false;
>  module_param_cb(disable_send_metrics, &param_ops_metrics, &disable_send_metrics, 0644);
>  MODULE_PARM_DESC(disable_send_metrics, "Enable sending perf metrics to ceph cluster (default: on)");
>  
> +/* for both v1 and v2 syntax */
> +bool mount_support = true;

This bool should be static too. I'll just make that change in-tree, so
you don't need to re-post.

Thanks,

> +static const struct kernel_param_ops param_ops_mount_syntax = {
> +	.get = param_get_bool,
> +};
> +module_param_cb(mount_syntax_v1, &param_ops_mount_syntax, &mount_support, 0444);
> +module_param_cb(mount_syntax_v2, &param_ops_mount_syntax, &mount_support, 0444);
> +
>  module_init(init_ceph);
>  module_exit(exit_ceph);
>  

-- 
Jeff Layton <jlayton@redhat.com>