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

[Ye Bin]

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@xxxxxxxxxx>
---
 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