[Qemu-devel] [PATCH 1/4] linux-user: Add support for sysfs() syscall

[Aleksandar Markovic]

From: Aleksandar Markovic <address@hidden>

This patch implements Qemu user mode sysfs() syscall support.

Syscall sysfs() involves returning information about the filesystem types
currently present in the kernel, and can operate in three distinct flavors,
depending on its first argument.

Its specific is that its declaration is threefold:

   int sysfs(int option, const char *fsname);
   int sysfs(int option, unsigned int fs_index, char *buf);
   int sysfs(int option);

Its implementation in Linux kernel is at fs/filesystems.c, line 184.

The implementation in Qemu user mode is based on invocation of host's
sysfs(), and its key part is in the correspondent case segment of the
main switch statement of the function do_syscall(), in file
linux-user/syscalls.c. All necessary conversions of data structures
from target to host and from host to target are covered. Based on
the value of the first argument, three cases are distinguished, and
such conversions are implemented separately for each case.

Buffer needed for the second cases has size defined with preprocessor
constant FST_NAME_MAX, that is set to 32. .This is good enough for
virtually all practical purposes. In that bufer, a name of the type
of the filesystem is stored. It is the same string as the second
column of the content of /proc/filesyste, and it is rarely longer
than 10 bytes.

Relevant support for "-strace" option is also included (files
linux-user/strace.c and linux-user/strace.list).

This patch also fixes failures of LTP tests sysfs01, sysfs02, sysfs03,
sysfs04, sysfs05, and sysfs06, if executed in Qemu user mode.

Signed-off-by: Aleksandar Markovic <address@hidden>
---
 linux-user/strace.c    | 27 +++++++++++++++++++++++++++
 linux-user/strace.list |  2 +-
 linux-user/syscall.c   | 40 +++++++++++++++++++++++++++++++++++++---
 3 files changed, 65 insertions(+), 4 deletions(-)

diff --git a/linux-user/strace.c b/linux-user/strace.c
index 1e51360..d9d5858 100644
--- a/linux-user/strace.c
+++ b/linux-user/strace.c
@@ -2220,6 +2220,33 @@ print_kill(const struct syscallname *name,
 }
 #endif
 
+#ifdef TARGET_NR_sysfs
+static void
+print_sysfs(const struct syscallname *name,
+    abi_long arg0, abi_long arg1, abi_long arg2,
+    abi_long arg3, abi_long arg4, abi_long arg5)
+{
+    print_syscall_prologue(name);
+    /* arg0 is normally 1, 2, or 3 */
+    switch (arg0) {
+    case 1:
+        print_raw_param("%d", arg0, 0);
+        print_string(arg1, 1);
+        break;
+    case 2:
+        print_raw_param("%d", arg0, 0);
+        print_raw_param("%u", arg1, 0);
+        print_pointer(arg2, 1);
+        break;
+    /* if arg0 is 3, desired output is the same as default */
+    default:
+        print_raw_param("%d", arg0, 1);
+        break;
+    }
+    print_syscall_epilogue(name);
+}
+#endif
+
 /*
  * An array of all of the syscalls we know about
  */
diff --git a/linux-user/strace.list b/linux-user/strace.list
index 608f7e0..93bc9d0 100644
--- a/linux-user/strace.list
+++ b/linux-user/strace.list
@@ -1476,7 +1476,7 @@
 { TARGET_NR_sys_epoll_wait, "sys_epoll_wait" , NULL, NULL, NULL },
 #endif
 #ifdef TARGET_NR_sysfs
-{ TARGET_NR_sysfs, "sysfs" , NULL, NULL, NULL },
+{ TARGET_NR_sysfs, "sysfs" , NULL, print_sysfs, NULL },
 #endif
 #ifdef TARGET_NR_sysinfo
 { TARGET_NR_sysinfo, "sysinfo" , NULL, NULL, NULL },
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 0815f30..fe8042c 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -7379,7 +7379,7 @@ static int do_openat(void *cpu_env, int dirfd, const char 
*pathname, int flags,
 
     if (fake_open->filename) {
         const char *tmpdir;
-        char filename[PATH_MAX];
+        char filename[128];
         int fd, r;
 
         /* create temporary file to map stat to */
@@ -9560,9 +9560,43 @@ abi_long do_syscall(void *cpu_env, int num, abi_long 
arg1,
     case TARGET_NR_bdflush:
         goto unimplemented;
 #endif
-#ifdef TARGET_NR_sysfs
+#if defined(TARGET_NR_sysfs)
+#define FST_NAME_MAX 32
     case TARGET_NR_sysfs:
-        goto unimplemented;
+        switch (arg1) {
+        case 1:
+            {
+                p = lock_user_string(arg2);
+                if (!p) {
+                    goto efault;
+                }
+                ret = get_errno(syscall(__NR_sysfs, arg1, p));
+                unlock_user(p, arg2, 0);
+            }
+            break;
+        case 2:
+            {
+                char buf[FST_NAME_MAX];
+                memset(buf, 0, FST_NAME_MAX);
+                ret = get_errno(syscall(__NR_sysfs, arg1, arg2, buf));
+                if (!is_error(ret)) {
+                    int len = FST_NAME_MAX - 1;
+                    if (len > strlen(buf)) {
+                        len = strlen(buf);
+                    }
+                    if (copy_to_user(arg3, buf, len + 1) != 0) {
+                        goto efault;
+                    }
+                }
+            }
+            break;
+        case 3:
+            ret = get_errno(syscall(__NR_sysfs, arg1));
+            break;
+        default:
+            ret = -EINVAL;
+        }
+        break;
 #endif
     case TARGET_NR_personality:
         ret = get_errno(personality(arg1));
-- 
2.9.3