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

Ye Bin
2024-03-22T06:42:00Z

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