[PATCH 3/4] linux user: refactored is proc myself, added support for fd/<execfd>

[aladjev.andrew@gmail.com]

From: Andrew Aladjev <aladjev.andrew@gmail.com>

---
 linux-user/syscall.c      |  12 ++--
 linux-user/syscall_proc.c | 113 +++++++++++++++++++++++++++++++-------
 linux-user/syscall_proc.h |   5 +-
 3 files changed, 101 insertions(+), 29 deletions(-)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 0ead34b..00ae823 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -8067,18 +8067,18 @@ static int do_openat(void *cpu_env, int dirfd, const char *pathname, int flags,
         { "auxv", open_self_auxv, is_proc_myself },
         { "cmdline", open_self_cmdline, is_proc_myself },
 #if defined(HOST_WORDS_BIGENDIAN) != defined(TARGET_WORDS_BIGENDIAN)
-        { "/proc/net/route", open_net_route, is_proc },
+        { "net/route", open_net_route, is_proc },
 #endif
 #if defined(TARGET_SPARC) || defined(TARGET_HPPA)
-        { "/proc/cpuinfo", open_cpuinfo, is_proc },
+        { "cpuinfo", open_cpuinfo, is_proc },
 #endif
 #if defined(TARGET_M68K)
-        { "/proc/hardware", open_hardware, is_proc },
+        { "hardware", open_hardware, is_proc },
 #endif
         { NULL, NULL, NULL }
     };
 
-    if (is_proc_myself(pathname, "exe")) {
+    if (is_proc_myself_exe(pathname)) {
         return execfd;
     }
 
@@ -9603,7 +9603,7 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
             } else if (!arg3) {
                 /* Short circuit this for the magic exe check. */
                 ret = -TARGET_EINVAL;
-            } else if (is_proc_myself((const char *)p, "exe")) {
+            } else if (is_proc_myself_exe((const char *)p)) {
                 char real[PATH_MAX], *temp;
                 temp = realpath(exec_path, real);
                 /* Return value is # of bytes that we wrote to the buffer. */
@@ -9632,7 +9632,7 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
             p2 = lock_user(VERIFY_WRITE, arg3, arg4, 0);
             if (!p || !p2) {
                 ret = -TARGET_EFAULT;
-            } else if (is_proc_myself((const char *)p, "exe")) {
+            } else if (is_proc_myself_exe((const char *)p)) {
                 char real[PATH_MAX], *temp;
                 temp = realpath(exec_path, real);
                 ret = temp == NULL ? get_errno(-1) : strlen(real) ;
diff --git a/linux-user/syscall_proc.c b/linux-user/syscall_proc.c
index 34051a8..3cf986b 100644
--- a/linux-user/syscall_proc.c
+++ b/linux-user/syscall_proc.c
@@ -1,32 +1,103 @@
 #include "qemu/osdep.h"
+#include "elf.h"
 
 #include "syscall_proc.h"
+#include "qemu.h"
 
-int is_proc_myself(const char *filename, const char *entry)
+#define PROC "/proc/"
+#define SELF "self/"
+#define FD   "fd/"
+
+#define STARTS_WITH(path, CONSTANT) (              \
+    strlen(path) >= strlen(CONSTANT) &&            \
+    strncmp(path, CONSTANT, strlen(CONSTANT)) == 0 \
+)
+
+static inline char *scope_to_proc(const char *path)
 {
-    if (!strncmp(filename, "/proc/", strlen("/proc/"))) {
-        filename += strlen("/proc/");
-        if (!strncmp(filename, "self/", strlen("self/"))) {
-            filename += strlen("self/");
-        } else if (*filename >= '1' && *filename <= '9') {
-            char myself[80];
-            snprintf(myself, sizeof(myself), "%d/", getpid());
-            if (!strncmp(filename, myself, strlen(myself))) {
-                filename += strlen(myself);
-            } else {
-                return 0;
-            }
-        } else {
-            return 0;
-        }
-        if (!strcmp(filename, entry)) {
-            return 1;
+    if (STARTS_WITH(path, PROC)) {
+        return (char *)path + strlen(PROC);
+    }
+
+    return NULL;
+}
+
+static inline char *scope_to_proc_myself(const char *path)
+{
+    char *scope_path = scope_to_proc(path);
+    if (scope_path == NULL) {
+        return NULL;
+    }
+
+    if (STARTS_WITH(scope_path, SELF)) {
+        return scope_path + strlen(SELF);
+    }
+
+    if (strlen(scope_path) >= 1 &&
+        *scope_path >= '1' && *scope_path <= '9') {
+        char pid_path[80];
+        snprintf(pid_path, sizeof(pid_path), "%d/", getpid());
+        if (STARTS_WITH(scope_path, pid_path)) {
+            return scope_path + strlen(pid_path);
         }
     }
-    return 0;
+
+    return NULL;
+}
+
+int is_proc(const char *path, const char *entry)
+{
+    char *scope_path = scope_to_proc(path);
+    if (scope_path == NULL) {
+        return 0;
+    }
+
+    return strcmp(scope_path, entry) == 0;
 }
 
-int is_proc(const char *filename, const char *entry)
+int is_proc_myself(const char *path, const char *entry)
 {
-    return strcmp(filename, entry) == 0;
+    char *scope_path = scope_to_proc_myself(path);
+    if (scope_path == NULL) {
+        return 0;
+    }
+
+    return strcmp(scope_path, entry) == 0;
+}
+
+/*
+ * Kernel creates "fd/#{number}" link after opening "exe" link.
+ * Both "exe" and "fd/#{number}" can be used by application.
+ *
+ * Kernel can provide infinite amount of fd numbers.
+ * QEMU is going to always return single global execfd.
+ *
+ * So we need to check "exe" and "fd/#{execfd}" only.
+ */
+
+int is_proc_myself_exe(const char *path)
+{
+    char *scope_path = scope_to_proc_myself(path);
+    if (scope_path == NULL) {
+        return 0;
+    }
+
+    if (strcmp(scope_path, "exe") == 0) {
+        return 1;
+    }
+
+    if (STARTS_WITH(scope_path, FD)) {
+        scope_path += strlen(FD);
+
+        if (strlen(scope_path) >= 1 &&
+            *scope_path >= '1' && *scope_path <= '9') {
+            char execfd_path[80];
+            snprintf(execfd_path, sizeof(execfd_path), "%d", execfd);
+            if (strcmp(scope_path, execfd_path) == 0) {
+                return 1;
+            }
+        }
+    }
+
+    return 0;
 }
diff --git a/linux-user/syscall_proc.h b/linux-user/syscall_proc.h
index 3098af9..f0e59c0 100644
--- a/linux-user/syscall_proc.h
+++ b/linux-user/syscall_proc.h
@@ -1,7 +1,8 @@
 #ifndef SYSCALL_PROC_H
 #define SYSCALL_PROC_H
 
-int is_proc(const char *filename, const char *entry);
-int is_proc_myself(const char *filename, const char *entry);
+int is_proc(const char *path, const char *entry);
+int is_proc_myself(const char *path, const char *entry);
+int is_proc_myself_exe(const char *path);
 
 #endif
-- 
2.26.2