fs: Implement lstat function

specified here:
https://pubs.opengroup.org/onlinepubs/009695399/functions/lstat.html

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>
Change-Id: Iefc23a02d425ff84fa4027aea7da1181b01eced7

fs/inode/inode.h

@@ -248,9 +248,10 @@ int inode_find(FAR struct inode_search_s *desc);
  *   <sys/stat.h>, into which information is placed concerning the file.
  *
  * Input Parameters:
- *   inode - The indoe of interest
+ *   inode   - The inode of interest
- *   buf   - The caller provide location in which to return information about
+ *   buf     - The caller provide location in which to return information
- *           the inode.
+ *             about the inode.
+ *   resolve - Whether to resolve the symbolic link
  *
  * Returned Value:
  *   Zero (OK) returned on success.  Otherwise, a negated errno value is
@@ -259,7 +260,7 @@ int inode_find(FAR struct inode_search_s *desc);
  ****************************************************************************/
 
 struct stat;  /* Forward reference */
-int inode_stat(FAR struct inode *inode, FAR struct stat *buf);
+int inode_stat(FAR struct inode *inode, FAR struct stat *buf, int resolve);
 
 /****************************************************************************
  * Name: inode_free

fs/mount/fs_automount.c

@@ -104,7 +104,7 @@ static int  automount_interrupt(FAR const struct automount_lower_s *lower,
  *
  * Returned Value:
  *   OK_EXIST if the inode exists
- *   OK_NOENT if the indoe does not exist
+ *   OK_NOENT if the inode does not exist
  *   Negated errno if some failure occurs
  *
  ****************************************************************************/

fs/vfs/fs_fstat.c

@@ -199,7 +199,7 @@ int file_fstat(FAR struct file *filep, FAR struct stat *buf)
         {
           /* The inode is part of the root pseudo file system. */
 
-          ret = inode_stat(inode, buf);
+          ret = inode_stat(inode, buf, 1);
         }
     }
 

fs/vfs/fs_stat.c

@@ -58,7 +58,7 @@
  ****************************************************************************/
 
 static inline int statroot(FAR struct stat *buf);
-int stat_recursive(FAR const char *path, FAR struct stat *buf);
+int stat_recursive(FAR const char *path, FAR struct stat *buf, int resolve);
 
 /****************************************************************************
  * Private Functions
@@ -93,7 +93,7 @@ static inline int statroot(FAR struct stat *buf)
  *
  ****************************************************************************/
 
-int stat_recursive(FAR const char *path, FAR struct stat *buf)
+int stat_recursive(FAR const char *path, FAR struct stat *buf, int resolve)
 {
   struct inode_search_s desc;
   FAR struct inode *inode;
@@ -143,7 +143,7 @@ int stat_recursive(FAR const char *path, FAR struct stat *buf)
        * recurse if soft links are supported in the pseudo file system.
        */
 
-      ret = inode_stat(inode, buf);
+      ret = inode_stat(inode, buf, resolve);
     }
 
   inode_release(inode);
@@ -171,7 +171,7 @@ errout_with_search:
  *
  ****************************************************************************/
 
-int nx_stat(FAR const char *path, FAR struct stat *buf)
+int nx_stat(FAR const char *path, FAR struct stat *buf, int resolve)
 {
   /* Sanity checks */
 
@@ -199,7 +199,7 @@ int nx_stat(FAR const char *path, FAR struct stat *buf)
 #ifdef CONFIG_PSEUDOFS_SOFTLINKS
   buf->st_count = 0;
 #endif
-  return stat_recursive(path, buf);
+  return stat_recursive(path, buf, resolve);
 }
 
 /****************************************************************************
@@ -222,7 +222,21 @@ int stat(FAR const char *path, FAR struct stat *buf)
 {
   int ret;
 
-  ret = nx_stat(path, buf);
+  ret = nx_stat(path, buf, 1);
+  if (ret < 0)
+    {
+      set_errno(-ret);
+      ret = ERROR;
+    }
+
+  return ret;
+}
+
+int lstat(FAR const char *path, FAR struct stat *buf)
+{
+  int ret;
+
+  ret = nx_stat(path, buf, 0);
   if (ret < 0)
     {
       set_errno(-ret);
@@ -243,9 +257,10 @@ int stat(FAR const char *path, FAR struct stat *buf)
  *   <sys/stat.h>, into which information is placed concerning the file.
  *
  * Input Parameters:
- *   inode - The indoe of interest
+ *   inode   - The inode of interest
- *   buf   - The caller provide location in which to return information about
+ *   buf     - The caller provide location in which to return information
- *           the inode.
+ *             about the inode.
+ *   resolve - Whether to resolve the symbolic link
  *
  * Returned Value:
  *   Zero (OK) returned on success.  Otherwise, a negated errno value is
@@ -253,7 +268,7 @@ int stat(FAR const char *path, FAR struct stat *buf)
  *
  ****************************************************************************/
 
-int inode_stat(FAR struct inode *inode, FAR struct stat *buf)
+int inode_stat(FAR struct inode *inode, FAR struct stat *buf, int resolve)
 {
   DEBUGASSERT(inode != NULL && buf != NULL);
 
@@ -321,42 +336,47 @@ int inode_stat(FAR struct inode *inode, FAR struct stat *buf)
 
       if (INODE_IS_SOFTLINK(inode))
         {
-          int ret;
+          if (resolve)
-
-          /* Increment the link counter.  This is necessary to avoid
-           * infinite recursion if loops are encountered in the traversal.
-           * If we encounter more SYMLOOP_MAX symbolic links at any time
-           * during the traversal, error out.
-           *
-           * NOTE: That inode_search() will automatically skip over
-           * consecutive, intermediate symbolic links.  Those numbers will
-           * not be included in the total.
-           */
-
-          if (++buf->st_count > SYMLOOP_MAX)
             {
-              return -ELOOP;
+              int ret;
+
+              /* Increment the link counter.  This is necessary to avoid
+               * infinite recursion if loops are encountered in the
+               * traversal. If we encounter more SYMLOOP_MAX symbolic links
+               * at any time during the traversal, error out.
+               *
+               * NOTE: That inode_search() will automatically skip over
+               * consecutive, intermediate symbolic links.  Those numbers
+               * will not be included in the total.
+               */
+
+              if (++buf->st_count > SYMLOOP_MAX)
+                {
+                  return -ELOOP;
+                }
+
+              DEBUGASSERT(buf->st_count > 0);  /* Check for unsigned integer overflow */
+
+              /* stat() the target of the soft link. */
+
+              ret = stat_recursive(inode->u.i_link, buf, 1);
+
+              /* If stat() fails, then there is a problem with the target of
+               * the symbolic link, but not with the symbolic link itself.
+               * We should still report success, just with less information.
+               */
+
+              if (ret < 0)
+                {
+                  RESET_BUF(buf);
+                }
             }
-
+          else
-          DEBUGASSERT(buf->st_count > 0);  /* Check for unsigned integer overflow */
-
-          /* stat() the target of the soft link. */
-
-          ret = stat_recursive((FAR const char *)inode->u.i_link, buf);
-
-          /* If stat() fails, then there is a problem with the target of the
-           * symbolic link, but not with the symbolic link itself.  We should
-           * still report success, just with less information.
-           */
-
-          if (ret < 0)
             {
-              RESET_BUF(buf);
+              /* Make sure the caller knows that this is a symbolic link. */
+
+              buf->st_mode |= S_IFLNK;
             }
-
-          /* Make sure the caller knows that this really a symbolic link. */
-
-          buf->st_mode |= S_IFLNK;
         }
       else
 #endif

include/nuttx/fs/fs.h

@@ -78,7 +78,7 @@
 #  define _NX_WRITE(f,b,s)     nx_write(f,b,s)
 #  define _NX_SEEK(f,o,w)      nx_seek(f,o,w)
 #  define _NX_IOCTL(f,r,a)     nx_ioctl(f,r,a)
-#  define _NX_STAT(p,s)        nx_stat(p,s)
+#  define _NX_STAT(p,s)        nx_stat(p,s,1)
 #  define _NX_GETERRNO(r)      (-(r))
 #  define _NX_SETERRNO(r)      set_errno(-(r))
 #  define _NX_GETERRVAL(r)     (r)
@@ -1450,7 +1450,7 @@ int file_fstat(FAR struct file *filep, FAR struct stat *buf);
  *
  ****************************************************************************/
 
-int nx_stat(FAR const char *path, FAR struct stat *buf);
+int nx_stat(FAR const char *path, FAR struct stat *buf, int resolve);
 
 #undef EXTERN
 #if defined(__cplusplus)

include/sys/stat.h

@@ -156,6 +156,7 @@ extern "C"
 int mkdir(FAR const char *pathname, mode_t mode);
 int mkfifo(FAR const char *pathname, mode_t mode);
 int stat(FAR const char *path, FAR struct stat *buf);
+int lstat(FAR const char *path, FAR struct stat *buf);
 int fstat(int fd, FAR struct stat *buf);
 int chmod(FAR const char *path, mode_t mode);
 int fchmod(int fd, mode_t mode);

include/sys/syscall_lookup.h

@@ -235,6 +235,7 @@ SYSCALL_LOOKUP(readdir,                    1)
 SYSCALL_LOOKUP(rewinddir,                  1)
 SYSCALL_LOOKUP(seekdir,                    2)
 SYSCALL_LOOKUP(stat,                       2)
+SYSCALL_LOOKUP(lstat,                      2)
 SYSCALL_LOOKUP(fstat,                      2)
 SYSCALL_LOOKUP(statfs,                     2)
 SYSCALL_LOOKUP(fstatfs,                    2)

syscall/syscall.csv

@@ -45,6 +45,7 @@
 "link","unistd.h","defined(CONFIG_PSEUDOFS_SOFTLINKS)","int","FAR const char *","FAR const char *"
 "listen","sys/socket.h","defined(CONFIG_NET)","int","int","int"
 "lseek","unistd.h","","off_t","int","off_t","int"
+"lstat","sys/stat.h","","int","FAR const char *","FAR struct stat *"
 "mkdir","sys/stat.h","!defined(CONFIG_DISABLE_MOUNTPOINT)","int","FAR const char *","mode_t"
 "mmap","sys/mman.h","","FAR void *","FAR void *","size_t","int","int","int","off_t"
 "modhandle","nuttx/module.h","defined(CONFIG_MODULE)","FAR void *","FAR const char *"