@matheusbsbs / matheus-bagliano
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1 #include "git-compat-util.h"
2
3 #include "strbuf.h"
4 #include "strvec.h"
5 #include "trace2.h"
6
7 /*
8 * We need more complex parsing in stat_parent_pid() and
9 * parse_proc_stat() below than a dumb fscanf(). That's because while
10 * the statcomm field is surrounded by parentheses, the process itself
11 * is free to insert any arbitrary byte sequence its its name. That
12 * can include newlines, spaces, closing parentheses etc.
13 *
14 * See do_task_stat() in fs/proc/array.c in linux.git, this is in
15 * contrast with the escaped version of the name found in
16 * /proc/%d/status.
17 *
18 * So instead of using fscanf() we'll read N bytes from it, look for
19 * the first "(", and then the last ")", anything in-between is our
20 * process name.
21 *
22 * How much N do we need? On Linux /proc/sys/kernel/pid_max is 2^15 by
23 * default, but it can be raised set to values of up to 2^22. So
24 * that's 7 digits for a PID. We have 2 PIDs in the first four fields
25 * we're interested in, so 2 * 7 = 14.
26 *
27 * We then have 3 spaces between those four values, and we'd like to
28 * get to the space between the 4th and the 5th (the "pgrp" field) to
29 * make sure we read the entire "ppid" field. So that brings us up to
30 * 14 + 3 + 1 = 18. Add the two parentheses around the "comm" value
31 * and it's 20. The "state" value itself is then one character (now at
32 * 21).
33 *
34 * Finally the maximum length of the "comm" name itself is 15
35 * characters, e.g. a setting of "123456789abcdefg" will be truncated
36 * to "123456789abcdef". See PR_SET_NAME in prctl(2). So all in all
37 * we'd need to read 21 + 15 = 36 bytes.
38 *
39 * Let's just read 2^6 (64) instead for good measure. If PID_MAX ever
40 * grows past 2^22 we'll be future-proof. We'll then anchor at the
41 * last ")" we find to locate the parent PID.
42 */
43 #define STAT_PARENT_PID_READ_N 64
44
45 static int parse_proc_stat(struct strbuf *sb, struct strbuf *name,
46 int *statppid)
47 {
48 const char *comm_lhs = strchr(sb->buf, '(');
49 const char *comm_rhs = strrchr(sb->buf, ')');
50 const char *ppid_lhs, *ppid_rhs;
51 char *p;
52 pid_t ppid;
53
54 if (!comm_lhs || !comm_rhs)
55 goto bad_kernel;
56
57 /*
58 * We're at the ")", that's followed by " X ", where X is a
59 * single "state" character. So advance by 4 bytes.
60 */
61 ppid_lhs = comm_rhs + 4;
62
63 /*
64 * Read until the space between the "ppid" and "pgrp" fields
65 * to make sure we're anchored after the untruncated "ppid"
66 * field..
67 */
68 ppid_rhs = strchr(ppid_lhs, ' ');
69 if (!ppid_rhs)
70 goto bad_kernel;
71
72 ppid = strtol(ppid_lhs, &p, 10);
73 if (ppid_rhs == p) {
74 const char *comm = comm_lhs + 1;
75 size_t commlen = comm_rhs - comm;
76
77 strbuf_add(name, comm, commlen);
78 *statppid = ppid;
79
80 return 0;
81 }
82
83 bad_kernel:
84 /*
85 * We were able to read our STAT_PARENT_PID_READ_N bytes from
86 * /proc/%d/stat, but the content is bad. Broken kernel?
87 * Should not happen, but handle it gracefully.
88 */
89 return -1;
90 }
91
92 static int stat_parent_pid(pid_t pid, struct strbuf *name, int *statppid)
93 {
94 struct strbuf procfs_path = STRBUF_INIT;
95 struct strbuf sb = STRBUF_INIT;
96 FILE *fp;
97 int ret = -1;
98
99 /* try to use procfs if it's present. */
100 strbuf_addf(&procfs_path, "/proc/%d/stat", pid);
101 fp = fopen(procfs_path.buf, "r");
102 if (!fp)
103 goto cleanup;
104
105 /*
106 * We could be more strict here and assert that we read at
107 * least STAT_PARENT_PID_READ_N. My reading of procfs(5) is
108 * that on any modern kernel (at least since 2.6.0 released in
109 * 2003) even if all the mandatory numeric fields were zero'd
110 * out we'd get at least 100 bytes, but let's just check that
111 * we got anything at all and trust the parse_proc_stat()
112 * function to handle its "Bad Kernel?" error checking.
113 */
114 if (!strbuf_fread(&sb, STAT_PARENT_PID_READ_N, fp))
115 goto cleanup;
116 if (parse_proc_stat(&sb, name, statppid) < 0)
117 goto cleanup;
118
119 ret = 0;
120 cleanup:
121 if (fp)
122 fclose(fp);
123 strbuf_release(&procfs_path);
124 strbuf_release(&sb);
125
126 return ret;
127 }
128
129 static void push_ancestry_name(struct strvec *names, pid_t pid)
130 {
131 struct strbuf name = STRBUF_INIT;
132 int ppid;
133
134 if (stat_parent_pid(pid, &name, &ppid) < 0)
135 goto cleanup;
136
137 strvec_push(names, name.buf);
138
139 /*
140 * Both errors and reaching the end of the process chain are
141 * reported as fields of 0 by proc(5)
142 */
143 if (ppid)
144 push_ancestry_name(names, ppid);
145 cleanup:
146 strbuf_release(&name);
147
148 return;
149 }
150
151 void trace2_collect_process_info(enum trace2_process_info_reason reason)
152 {
153 struct strvec names = STRVEC_INIT;
154
155 if (!trace2_is_enabled())
156 return;
157
158 switch (reason) {
159 case TRACE2_PROCESS_INFO_EXIT:
160 /*
161 * The Windows version of this calls its
162 * get_peak_memory_info() here. We may want to insert
163 * similar process-end statistics here in the future.
164 */
165 break;
166 case TRACE2_PROCESS_INFO_STARTUP:
167 push_ancestry_name(&names, getppid());
168
169 if (names.nr)
170 trace2_cmd_ancestry(names.v);
171 strvec_clear(&names);
172 break;
173 }
174
175 return;
176 }