Re: [PATCH v8 2/5] tracing/probes: support '%pD' type for print struct file's name

Masami Hiramatsu
2024-03-25T00:40:57Z

On Fri, 22 Mar 2024 14:43:05 +0800
Ye Bin <yebin10@huawei.com> wrote:

> As like previous patch, this patch support print type '%pD' for print file's

nit: Note that "previous patch" is obscure after it is merged with other patches
in other trees/branches. So it should be "As like %pd".

Anyway, let me change it.

Thank you,

> name. For example "name=$arg1:%pD" casts the `$arg1` as (struct file*),
> dereferences the "file.f_path.dentry.d_name.name" field and stores it to
> "name" argument as a kernel string.
> Here is an example:
> [tracing]# echo 'p:testprobe vfs_read name=$arg1:%pD' > kprobe_event
> [tracing]# echo 1 > events/kprobes/testprobe/enable
> [tracing]# grep -q "1" events/kprobes/testprobe/enable
> [tracing]# echo 0 > events/kprobes/testprobe/enable
> [tracing]# grep "vfs_read" trace | grep "enable"
> grep-15108 [003] ..... 5228.328609: testprobe: (vfs_read+0x4/0xbb0) name="enable"
>
> Note that this expects the given argument (e.g. $arg1) is an address of struct
> file. User must ensure it.
>
> Signed-off-by: Ye Bin <yebin10@huawei.com>
> ---
> kernel/trace/trace.c | 2 +-
> kernel/trace/trace_probe.c | 57 +++++++++++++++++++++++---------------
> 2 files changed, 36 insertions(+), 23 deletions(-)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index ac26b8446337..831dfd0773a4 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -5510,7 +5510,7 @@ static const char readme_msg[] =
> "\t +|-[u]<offset>(<fetcharg>), \\imm-value, \\\"imm-string\"\n"
> "\t type: s8/16/32/64, u8/16/32/64, x8/16/32/64, char, string, symbol,\n"
> "\t b<bit-width>@<bit-offset>/<container-size>, ustring,\n"
> - "\t symstr, %pd, <type>\\[<array-size>\\]\n"
> + "\t symstr, %pd/%pD, <type>\\[<array-size>\\]\n"
> #ifdef CONFIG_HIST_TRIGGERS
> "\t field: <stype> <name>;\n"
> "\t stype: u8/u16/u32/u64, s8/s16/s32/s64, pid_t,\n"
> diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
> index a27567e16c36..7bfc6c0d5436 100644
> --- a/kernel/trace/trace_probe.c
> +++ b/kernel/trace/trace_probe.c
> @@ -12,6 +12,7 @@
> #define pr_fmt(fmt) "trace_probe: " fmt
>
> #include <linux/bpf.h>
> +#include <linux/fs.h>
> #include "trace_btf.h"
>
> #include "trace_probe.h"
> @@ -1581,35 +1582,47 @@ int traceprobe_expand_dentry_args(int argc, const char *argv[], char **buf)
>
> used = 0;
> for (i = 0; i < argc; i++) {
> - if (glob_match("*:%pd", argv[i])) {
> - char *tmp;
> - char *equal;
> -
> - if (!tmpbuf) {
> - tmpbuf = kmalloc(bufsize, GFP_KERNEL);
> - if (!tmpbuf)
> - return -ENOMEM;
> - }
> + char *tmp;
> + char *equal;
> + size_t arg_len;
>
> - tmp = kstrdup(argv[i], GFP_KERNEL);
> - if (!tmp)
> - goto nomem;
> + if (!glob_match("*:%p[dD]", argv[i]))
> + continue;
>
> - equal = strchr(tmp, '=');
> - if (equal)
> - *equal = '\0';
> - tmp[strlen(argv[i]) - 4] = '\0';
> + if (!tmpbuf) {
> + tmpbuf = kmalloc(bufsize, GFP_KERNEL);
> + if (!tmpbuf)
> + return -ENOMEM;
> + }
> +
> + tmp = kstrdup(argv[i], GFP_KERNEL);
> + if (!tmp)
> + goto nomem;
> +
> + equal = strchr(tmp, '=');
> + if (equal)
> + *equal = '\0';
> + arg_len = strlen(argv[i]);
> + tmp[arg_len - 4] = '\0';
> + if (argv[i][arg_len - 1] == 'd')
> ret = snprintf(tmpbuf + used, bufsize - used,
> "%s%s+0x0(+0x%zx(%s)):string",
> equal ? tmp : "", equal ? "=" : "",
> offsetof(struct dentry, d_name.name),
> equal ? equal + 1 : tmp);
> - kfree(tmp);
> - if (ret >= bufsize - used)
> - goto nomem;
> - argv[i] = tmpbuf + used;
> - used += ret + 1;
> - }
> + else
> + ret = snprintf(tmpbuf + used, bufsize - used,
> + "%s%s+0x0(+0x%zx(+0x%zx(%s))):string",
> + equal ? tmp : "", equal ? "=" : "",
> + offsetof(struct dentry, d_name.name),
> + offsetof(struct file, f_path.dentry),
> + equal ? equal + 1 : tmp);
> +
> + kfree(tmp);
> + if (ret >= bufsize - used)
> + goto nomem;
> + argv[i] = tmpbuf + used;
> + used += ret + 1;
> }
>
> *buf = tmpbuf;
> --
> 2.31.1
>

--
Masami Hiramatsu (Google) <mhiramat@kernel.org>