[PATCH] btf: Use BIN_ATTR_SIMPLE_RO() to define vmlinux attribute

[PATCH] btf: Use BIN_ATTR_SIMPLE_RO() to define vmlinux attribute

[Thomas Weißschuh]

The usage of the macro allows to remove the custom handler function,
saving some memory. Additionally the code is easier to read.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
Something similar can be done to btf_module_read() in kernel/bpf/btf.c.
But doing it here and now would lead to some conflicts with some other
sysfs refactorings I'm doing. It will be part of a future series.
---
 kernel/bpf/sysfs_btf.c | 21 +++++----------------
 1 file changed, 5 insertions(+), 16 deletions(-)

diff --git a/kernel/bpf/sysfs_btf.c b/kernel/bpf/sysfs_btf.c
index fedb54c94cdb830a4890d33677dcc5a6e236c13f..a24381f933d0b80b11116d05463c35e9fa66acb1 100644
--- a/kernel/bpf/sysfs_btf.c
+++ b/kernel/bpf/sysfs_btf.c
@@ -12,34 +12,23 @@
 extern char __start_BTF[];
 extern char __stop_BTF[];
 
-static ssize_t
-btf_vmlinux_read(struct file *file, struct kobject *kobj,
-		 struct bin_attribute *bin_attr,
-		 char *buf, loff_t off, size_t len)
-{
-	memcpy(buf, __start_BTF + off, len);
-	return len;
-}
-
-static struct bin_attribute bin_attr_btf_vmlinux __ro_after_init = {
-	.attr = { .name = "vmlinux", .mode = 0444, },
-	.read = btf_vmlinux_read,
-};
+static __ro_after_init BIN_ATTR_SIMPLE_RO(vmlinux);
 
 struct kobject *btf_kobj;
 
 static int __init btf_vmlinux_init(void)
 {
-	bin_attr_btf_vmlinux.size = __stop_BTF - __start_BTF;
+	bin_attr_vmlinux.private = __start_BTF;
+	bin_attr_vmlinux.size = __stop_BTF - __start_BTF;
 
-	if (bin_attr_btf_vmlinux.size == 0)
+	if (bin_attr_vmlinux.size == 0)
 		return 0;
 
 	btf_kobj = kobject_create_and_add("btf", kernel_kobj);
 	if (!btf_kobj)
 		return -ENOMEM;
 
-	return sysfs_create_bin_file(btf_kobj, &bin_attr_btf_vmlinux);
+	return sysfs_create_bin_file(btf_kobj, &bin_attr_vmlinux);
 }
 
 subsys_initcall(btf_vmlinux_init);

---
base-commit: 28eb75e178d389d325f1666e422bc13bbbb9804c
change-id: 20241122-sysfs-const-bin_attr-bpf-737286bb9f27

Best regards,
-- 
Thomas Weißschuh <linux@weissschuh.net>

Re: [PATCH] btf: Use BIN_ATTR_SIMPLE_RO() to define vmlinux attribute

[Andrii Nakryiko]

On Fri, Nov 22, 2024 at 4:57 AM Thomas Weißschuh <linux@weissschuh.net> wrote:
>
> The usage of the macro allows to remove the custom handler function,
> saving some memory. Additionally the code is easier to read.
>
> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> ---
> Something similar can be done to btf_module_read() in kernel/bpf/btf.c.
> But doing it here and now would lead to some conflicts with some other
> sysfs refactorings I'm doing. It will be part of a future series.
> ---
>  kernel/bpf/sysfs_btf.c | 21 +++++----------------
>  1 file changed, 5 insertions(+), 16 deletions(-)
>

Nice, let's simplify. But why change the name to generic "vmlinux" if
it's actually btf_vmlinux? Can we keep the original btf-specific name?

pw-bot: cr

> diff --git a/kernel/bpf/sysfs_btf.c b/kernel/bpf/sysfs_btf.c
> index fedb54c94cdb830a4890d33677dcc5a6e236c13f..a24381f933d0b80b11116d05463c35e9fa66acb1 100644
> --- a/kernel/bpf/sysfs_btf.c
> +++ b/kernel/bpf/sysfs_btf.c
> @@ -12,34 +12,23 @@
>  extern char __start_BTF[];
>  extern char __stop_BTF[];
>
> -static ssize_t
> -btf_vmlinux_read(struct file *file, struct kobject *kobj,
> -                struct bin_attribute *bin_attr,
> -                char *buf, loff_t off, size_t len)
> -{
> -       memcpy(buf, __start_BTF + off, len);
> -       return len;
> -}
> -
> -static struct bin_attribute bin_attr_btf_vmlinux __ro_after_init = {
> -       .attr = { .name = "vmlinux", .mode = 0444, },
> -       .read = btf_vmlinux_read,
> -};
> +static __ro_after_init BIN_ATTR_SIMPLE_RO(vmlinux);
>
>  struct kobject *btf_kobj;
>
>  static int __init btf_vmlinux_init(void)
>  {
> -       bin_attr_btf_vmlinux.size = __stop_BTF - __start_BTF;
> +       bin_attr_vmlinux.private = __start_BTF;
> +       bin_attr_vmlinux.size = __stop_BTF - __start_BTF;
>
> -       if (bin_attr_btf_vmlinux.size == 0)
> +       if (bin_attr_vmlinux.size == 0)
>                 return 0;
>
>         btf_kobj = kobject_create_and_add("btf", kernel_kobj);
>         if (!btf_kobj)
>                 return -ENOMEM;
>
> -       return sysfs_create_bin_file(btf_kobj, &bin_attr_btf_vmlinux);
> +       return sysfs_create_bin_file(btf_kobj, &bin_attr_vmlinux);
>  }
>
>  subsys_initcall(btf_vmlinux_init);
>
> ---
> base-commit: 28eb75e178d389d325f1666e422bc13bbbb9804c
> change-id: 20241122-sysfs-const-bin_attr-bpf-737286bb9f27
>
> Best regards,
> --
> Thomas Weißschuh <linux@weissschuh.net>
>

Re: [PATCH] btf: Use BIN_ATTR_SIMPLE_RO() to define vmlinux attribute

[Thomas Weißschuh]

On 2024-11-26 13:37:26-0800, Andrii Nakryiko wrote:
> On Fri, Nov 22, 2024 at 4:57 AM Thomas Weißschuh <linux@weissschuh.net> wrote:
> >
> > The usage of the macro allows to remove the custom handler function,
> > saving some memory. Additionally the code is easier to read.
> >
> > Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> > ---
> > Something similar can be done to btf_module_read() in kernel/bpf/btf.c.
> > But doing it here and now would lead to some conflicts with some other
> > sysfs refactorings I'm doing. It will be part of a future series.
> > ---
> >  kernel/bpf/sysfs_btf.c | 21 +++++----------------
> >  1 file changed, 5 insertions(+), 16 deletions(-)
> >
> 
> Nice, let's simplify. But why change the name to generic "vmlinux" if
> it's actually btf_vmlinux? Can we keep the original btf-specific name?

The file in sysfs is named "vmlinux", /sys/kernel/btf/vmlinux.
This is what needs to be passed to the macro, it will name both the
variable and the file after it.

One alternative would be to use __BIN_ATTR_SIMPLE_RO() which allows a
custom name.

> 
> pw-bot: cr
> 
> > diff --git a/kernel/bpf/sysfs_btf.c b/kernel/bpf/sysfs_btf.c
> > index fedb54c94cdb830a4890d33677dcc5a6e236c13f..a24381f933d0b80b11116d05463c35e9fa66acb1 100644
> > --- a/kernel/bpf/sysfs_btf.c
> > +++ b/kernel/bpf/sysfs_btf.c
> > @@ -12,34 +12,23 @@
> >  extern char __start_BTF[];
> >  extern char __stop_BTF[];
> >
> > -static ssize_t
> > -btf_vmlinux_read(struct file *file, struct kobject *kobj,
> > -                struct bin_attribute *bin_attr,
> > -                char *buf, loff_t off, size_t len)
> > -{
> > -       memcpy(buf, __start_BTF + off, len);
> > -       return len;
> > -}
> > -
> > -static struct bin_attribute bin_attr_btf_vmlinux __ro_after_init = {
> > -       .attr = { .name = "vmlinux", .mode = 0444, },
> > -       .read = btf_vmlinux_read,
> > -};
> > +static __ro_after_init BIN_ATTR_SIMPLE_RO(vmlinux);
> >
> >  struct kobject *btf_kobj;
> >
> >  static int __init btf_vmlinux_init(void)
> >  {
> > -       bin_attr_btf_vmlinux.size = __stop_BTF - __start_BTF;
> > +       bin_attr_vmlinux.private = __start_BTF;
> > +       bin_attr_vmlinux.size = __stop_BTF - __start_BTF;
> >
> > -       if (bin_attr_btf_vmlinux.size == 0)
> > +       if (bin_attr_vmlinux.size == 0)
> >                 return 0;
> >
> >         btf_kobj = kobject_create_and_add("btf", kernel_kobj);
> >         if (!btf_kobj)
> >                 return -ENOMEM;
> >
> > -       return sysfs_create_bin_file(btf_kobj, &bin_attr_btf_vmlinux);
> > +       return sysfs_create_bin_file(btf_kobj, &bin_attr_vmlinux);
> >  }
> >
> >  subsys_initcall(btf_vmlinux_init);
> >
> > ---
> > base-commit: 28eb75e178d389d325f1666e422bc13bbbb9804c
> > change-id: 20241122-sysfs-const-bin_attr-bpf-737286bb9f27
> >
> > Best regards,
> > --
> > Thomas Weißschuh <linux@weissschuh.net>
> >

Re: [PATCH] btf: Use BIN_ATTR_SIMPLE_RO() to define vmlinux attribute

[Andrii Nakryiko]

On Tue, Nov 26, 2024 at 1:42 PM Thomas Weißschuh <linux@weissschuh.net> wrote:
>
> On 2024-11-26 13:37:26-0800, Andrii Nakryiko wrote:
> > On Fri, Nov 22, 2024 at 4:57 AM Thomas Weißschuh <linux@weissschuh.net> wrote:
> > >
> > > The usage of the macro allows to remove the custom handler function,
> > > saving some memory. Additionally the code is easier to read.
> > >
> > > Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> > > ---
> > > Something similar can be done to btf_module_read() in kernel/bpf/btf.c.
> > > But doing it here and now would lead to some conflicts with some other
> > > sysfs refactorings I'm doing. It will be part of a future series.
> > > ---
> > >  kernel/bpf/sysfs_btf.c | 21 +++++----------------
> > >  1 file changed, 5 insertions(+), 16 deletions(-)
> > >
> >
> > Nice, let's simplify. But why change the name to generic "vmlinux" if
> > it's actually btf_vmlinux? Can we keep the original btf-specific name?
>
> The file in sysfs is named "vmlinux", /sys/kernel/btf/vmlinux.
> This is what needs to be passed to the macro, it will name both the
> variable and the file after it.
>
> One alternative would be to use __BIN_ATTR_SIMPLE_RO() which allows a
> custom name.
>

Probably not worth it, ok, I'm fine with the name change, it's a local
name anyways.

> >
> > pw-bot: cr
> >
> > > diff --git a/kernel/bpf/sysfs_btf.c b/kernel/bpf/sysfs_btf.c
> > > index fedb54c94cdb830a4890d33677dcc5a6e236c13f..a24381f933d0b80b11116d05463c35e9fa66acb1 100644
> > > --- a/kernel/bpf/sysfs_btf.c
> > > +++ b/kernel/bpf/sysfs_btf.c
> > > @@ -12,34 +12,23 @@
> > >  extern char __start_BTF[];
> > >  extern char __stop_BTF[];
> > >
> > > -static ssize_t
> > > -btf_vmlinux_read(struct file *file, struct kobject *kobj,
> > > -                struct bin_attribute *bin_attr,
> > > -                char *buf, loff_t off, size_t len)
> > > -{
> > > -       memcpy(buf, __start_BTF + off, len);
> > > -       return len;
> > > -}
> > > -
> > > -static struct bin_attribute bin_attr_btf_vmlinux __ro_after_init = {
> > > -       .attr = { .name = "vmlinux", .mode = 0444, },
> > > -       .read = btf_vmlinux_read,
> > > -};
> > > +static __ro_after_init BIN_ATTR_SIMPLE_RO(vmlinux);
> > >
> > >  struct kobject *btf_kobj;
> > >
> > >  static int __init btf_vmlinux_init(void)
> > >  {
> > > -       bin_attr_btf_vmlinux.size = __stop_BTF - __start_BTF;
> > > +       bin_attr_vmlinux.private = __start_BTF;
> > > +       bin_attr_vmlinux.size = __stop_BTF - __start_BTF;
> > >
> > > -       if (bin_attr_btf_vmlinux.size == 0)
> > > +       if (bin_attr_vmlinux.size == 0)
> > >                 return 0;
> > >
> > >         btf_kobj = kobject_create_and_add("btf", kernel_kobj);
> > >         if (!btf_kobj)
> > >                 return -ENOMEM;
> > >
> > > -       return sysfs_create_bin_file(btf_kobj, &bin_attr_btf_vmlinux);
> > > +       return sysfs_create_bin_file(btf_kobj, &bin_attr_vmlinux);
> > >  }
> > >
> > >  subsys_initcall(btf_vmlinux_init);
> > >
> > > ---
> > > base-commit: 28eb75e178d389d325f1666e422bc13bbbb9804c
> > > change-id: 20241122-sysfs-const-bin_attr-bpf-737286bb9f27
> > >
> > > Best regards,
> > > --
> > > Thomas Weißschuh <linux@weissschuh.net>
> > >

Re: [PATCH] btf: Use BIN_ATTR_SIMPLE_RO() to define vmlinux attribute

[Alexei Starovoitov]

On Fri, Nov 22, 2024 at 4:57 AM Thomas Weißschuh <linux@weissschuh.net> wrote:
>
> The usage of the macro allows to remove the custom handler function,
> saving some memory. Additionally the code is easier to read.
>
> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> ---
> Something similar can be done to btf_module_read() in kernel/bpf/btf.c.
> But doing it here and now would lead to some conflicts with some other
> sysfs refactorings I'm doing. It will be part of a future series.
> ---
>  kernel/bpf/sysfs_btf.c | 21 +++++----------------
>  1 file changed, 5 insertions(+), 16 deletions(-)
>
> diff --git a/kernel/bpf/sysfs_btf.c b/kernel/bpf/sysfs_btf.c
> index fedb54c94cdb830a4890d33677dcc5a6e236c13f..a24381f933d0b80b11116d05463c35e9fa66acb1 100644
> --- a/kernel/bpf/sysfs_btf.c
> +++ b/kernel/bpf/sysfs_btf.c
> @@ -12,34 +12,23 @@
>  extern char __start_BTF[];
>  extern char __stop_BTF[];
>
> -static ssize_t
> -btf_vmlinux_read(struct file *file, struct kobject *kobj,
> -                struct bin_attribute *bin_attr,
> -                char *buf, loff_t off, size_t len)
> -{
> -       memcpy(buf, __start_BTF + off, len);
> -       return len;
> -}
> -
> -static struct bin_attribute bin_attr_btf_vmlinux __ro_after_init = {
> -       .attr = { .name = "vmlinux", .mode = 0444, },
> -       .read = btf_vmlinux_read,
> -};
> +static __ro_after_init BIN_ATTR_SIMPLE_RO(vmlinux);

To be honest I really don't like when code is hidden by macros like this.
Looks like you guys already managed to sprinkle it in a few places.

btf_vmlinux_read() can be replaced with sysfs_bin_attr_simple_read().
This part is fine, but macro pls dont.
It doesn't help readability.
imo mode = 0444 vs mode = 0400 is easier to understand
instead of _RO vs _ADMIN_RO suffix.
__ro_after_init should be a part of it, at least.

I'd like to hear what other maintainers think about
such obfuscation.

Re: [PATCH] btf: Use BIN_ATTR_SIMPLE_RO() to define vmlinux attribute

[Thomas Weißschuh]

On 2024-11-26 17:52:29-0800, Alexei Starovoitov wrote:
> On Fri, Nov 22, 2024 at 4:57 AM Thomas Weißschuh <linux@weissschuh.net> wrote:
> >
> > The usage of the macro allows to remove the custom handler function,
> > saving some memory. Additionally the code is easier to read.
> >
> > Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> > ---
> > Something similar can be done to btf_module_read() in kernel/bpf/btf.c.
> > But doing it here and now would lead to some conflicts with some other
> > sysfs refactorings I'm doing. It will be part of a future series.
> > ---
> >  kernel/bpf/sysfs_btf.c | 21 +++++----------------
> >  1 file changed, 5 insertions(+), 16 deletions(-)
> >
> > diff --git a/kernel/bpf/sysfs_btf.c b/kernel/bpf/sysfs_btf.c
> > index fedb54c94cdb830a4890d33677dcc5a6e236c13f..a24381f933d0b80b11116d05463c35e9fa66acb1 100644
> > --- a/kernel/bpf/sysfs_btf.c
> > +++ b/kernel/bpf/sysfs_btf.c
> > @@ -12,34 +12,23 @@
> >  extern char __start_BTF[];
> >  extern char __stop_BTF[];
> >
> > -static ssize_t
> > -btf_vmlinux_read(struct file *file, struct kobject *kobj,
> > -                struct bin_attribute *bin_attr,
> > -                char *buf, loff_t off, size_t len)
> > -{
> > -       memcpy(buf, __start_BTF + off, len);
> > -       return len;
> > -}
> > -
> > -static struct bin_attribute bin_attr_btf_vmlinux __ro_after_init = {
> > -       .attr = { .name = "vmlinux", .mode = 0444, },
> > -       .read = btf_vmlinux_read,
> > -};
> > +static __ro_after_init BIN_ATTR_SIMPLE_RO(vmlinux);
> 
> To be honest I really don't like when code is hidden by macros like this.
> Looks like you guys already managed to sprinkle it in a few places.
> 
> btf_vmlinux_read() can be replaced with sysfs_bin_attr_simple_read().
> This part is fine, but macro pls dont.
> It doesn't help readability.
> imo mode = 0444 vs mode = 0400 is easier to understand
> instead of _RO vs _ADMIN_RO suffix.

I'm fine with either solution.

My patch is motivated by my current effort to constify 'struct
bin_attribute' throughout the kernel.
With the macro I only have to touch this location once,
without it twice.

If we go with a plain sysfs_bin_attr_simple_read() please let me do the
patch in another series I have prepared, to be submitted after 6.13-rc1.

> __ro_after_init should be a part of it, at least.

I see where you are coming from, it would break the pattern with all the
other attribute macros however.

> I'd like to hear what other maintainers think about
> such obfuscation.

Ack.