Re: [RFC PATCH 3/5] ebpf: Added declaration/initialization routines.

[Daniel P . Berrangé]

On Thu, Mar 30, 2023 at 03:15:20AM +0300, Andrew Melnychenko wrote:
> Now, the binary objects may be retrieved by id/name.
> It would require for future qmp commands that may require specific
> eBPF blob.
> 
> Signed-off-by: Andrew Melnychenko <andrew@daynix.com>
> ---
>  ebpf/ebpf.c      | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
>  ebpf/ebpf.h      | 25 +++++++++++++++++++++++++
>  ebpf/ebpf_rss.c  |  4 ++++
>  ebpf/meson.build |  1 +
>  4 files changed, 78 insertions(+)
>  create mode 100644 ebpf/ebpf.c
>  create mode 100644 ebpf/ebpf.h
> 
> diff --git a/ebpf/ebpf.c b/ebpf/ebpf.c
> new file mode 100644
> index 0000000000..86320d72f5
> --- /dev/null
> +++ b/ebpf/ebpf.c
> @@ -0,0 +1,48 @@
> +/*
> + * QEMU eBPF binary declaration routine.
> + *
> + * Developed by Daynix Computing LTD (http://www.daynix.com)
> + *
> + * Authors:
> + *  Andrew Melnychenko <andrew@daynix.com>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or
> + * later.  See the COPYING file in the top-level directory.
> + */
> +
> +#include "qemu/osdep.h"
> +#include "qemu/queue.h"
> +#include "ebpf/ebpf.h"
> +
> +struct ElfBinaryDataEntry {
> +    const char *id;
> +    const void * (*fn)(size_t *);

It feels odd to be storing the function there, as that's just
an artifact of how the EBPF rss program is acquired. IMHO
this should just be

   const void *data;
   size_t datalen;

> +
> +    QSLIST_ENTRY(ElfBinaryDataEntry) node;
> +};
> +
> +static QSLIST_HEAD(, ElfBinaryDataEntry) ebpf_elf_obj_list =
> +                                            QSLIST_HEAD_INITIALIZER();
> +
> +void ebpf_register_binary_data(const char *id, const void * (*fn)(size_t *))
> +{
> +    struct ElfBinaryDataEntry *data = NULL;
> +
> +    data = g_malloc0(sizeof(*data));

We prefer g_new0 over g_malloc and initialize when declaring eg

    struct ElfBinaryDataEntry *data = g_new0(struct ElfBinaryDataEntry, 1);

> +    data->fn = fn;
> +    data->id = id;
> +
> +    QSLIST_INSERT_HEAD(&ebpf_elf_obj_list, data, node);
> +}
> +
> +const void *ebpf_find_binary_by_id(const char *id, size_t *sz)
> +{
> +    struct ElfBinaryDataEntry *it = NULL;
> +    QSLIST_FOREACH(it, &ebpf_elf_obj_list, node) {
> +        if (strcmp(id, it->id) == 0) {
> +            return it->fn(sz);
> +        }
> +    }
> +
> +    return NULL;
> +}
> diff --git a/ebpf/ebpf.h b/ebpf/ebpf.h
> new file mode 100644
> index 0000000000..fd705cb73e
> --- /dev/null
> +++ b/ebpf/ebpf.h
> @@ -0,0 +1,25 @@
> +/*
> + * QEMU eBPF binary declaration routine.
> + *
> + * Developed by Daynix Computing LTD (http://www.daynix.com)
> + *
> + * Authors:
> + *  Andrew Melnychenko <andrew@daynix.com>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or
> + * later.  See the COPYING file in the top-level directory.
> + */
> +
> +#ifndef EBPF_H
> +#define EBPF_H
> +
> +void ebpf_register_binary_data(const char *id, const void * (*fn)(size_t *));

IMHO it would be better as

void ebpf_register_binary_data(const char *id, const void *data, size_t 
datalen);


> +const void *ebpf_find_binary_by_id(const char *id, size_t *sz);
> +
> +#define ebpf_binary_init(id, fn)                                           \
> +static void __attribute__((constructor)) ebpf_binary_init_ ## fn(void)     \
> +{                                                                          \
> +    ebpf_register_binary_data(id, fn);                                     \

size_t datalen;
const void *data = fn(&datalen);
ebpf_register_binary_data(oid, data, datalen);


> +}
> +
> +#endif /* EBPF_H */
> diff --git a/ebpf/ebpf_rss.c b/ebpf/ebpf_rss.c
> index 08015fecb1..b4038725f2 100644
> --- a/ebpf/ebpf_rss.c
> +++ b/ebpf/ebpf_rss.c
> @@ -21,6 +21,8 @@
>  
>  #include "ebpf/ebpf_rss.h"
>  #include "ebpf/rss.bpf.skeleton.h"
> +#include "ebpf/ebpf.h"
> +
>  #include "trace.h"
>  
>  void ebpf_rss_init(struct EBPFRSSContext *ctx)
> @@ -237,3 +239,5 @@ void ebpf_rss_unload(struct EBPFRSSContext *ctx)
>      ctx->obj = NULL;
>      ctx->program_fd = -1;
>  }
> +
> +ebpf_binary_init("rss", rss_bpf__elf_bytes)
> diff --git a/ebpf/meson.build b/ebpf/meson.build
> index 2dd0fd8948..67c3f53aa9 100644
> --- a/ebpf/meson.build
> +++ b/ebpf/meson.build
> @@ -1 +1,2 @@
> +softmmu_ss.add(files('ebpf.c'))
>  softmmu_ss.add(when: libbpf, if_true: files('ebpf_rss.c'), if_false: 
> files('ebpf_rss-stub.c'))
> -- 
> 2.39.1
> 

With regards,
Daniel
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