From a085a0a70b48fdf49957bd00c86c80dbf2d0d2e5 Mon Sep 17 00:00:00 2001
From: Juha Niskanen <juha.niskanen@haltian.com>
Date: Tue, 5 Nov 2019 07:32:23 -0600
Subject: [PATCH] fs/smartfs/smartfs_smart.c:  Honor O_APPEND on writes.  Also
 document pwrite() bug/limitation.

---
 fs/smartfs/smartfs_smart.c | 14 ++++++++++++++
 fs/smartfs/smartfs_utils.c |  4 ++--
 fs/vfs/fs_pwrite.c         |  6 ++++++
 3 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/fs/smartfs/smartfs_smart.c b/fs/smartfs/smartfs_smart.c
index 540c724e57..3e7d38c1ca 100644
--- a/fs/smartfs/smartfs_smart.c
+++ b/fs/smartfs/smartfs_smart.c
@@ -673,6 +673,20 @@ static ssize_t smartfs_write(FAR struct file *filep, const char *buffer,
       goto errout_with_semaphore;
     }
 
+  /* Test if we opened for APPEND mode.  If we did, then seek to the
+   * end of the file.
+   */
+
+  if (sf->oflags & O_APPEND)
+    {
+      ret = smartfs_seek_internal(fs, sf, 0, SEEK_END);
+      if (ret < 0)
+        {
+          ret = -EIO;
+          goto errout_with_semaphore;
+        }
+    }
+
   /* First test if we are overwriting an existing location or writing to
    * a new one.
    */
diff --git a/fs/smartfs/smartfs_utils.c b/fs/smartfs/smartfs_utils.c
index 003d49df70..c76f55fc8e 100644
--- a/fs/smartfs/smartfs_utils.c
+++ b/fs/smartfs/smartfs_utils.c
@@ -1901,7 +1901,7 @@ int smartfs_extendfile(FAR struct smartfs_mountpt_s *fs,
 
   /* Loop until either (1) the file has been fully extended with zeroed data
    * or (2) an error occurs.  We assume we start with the current sector in
-   * cache (ff_currentsector)
+   * cache (ff_currentsector).
    */
 
   oldsize   = sf->entry.datlen;
@@ -1909,7 +1909,7 @@ int smartfs_extendfile(FAR struct smartfs_mountpt_s *fs,
   DEBUGASSERT(length > oldsize);
 
   /* Seek to the end of the file for the append/write operation, remembering
-   * the current file position.  It will be retored before returneding; the
+   * the current file position.  It will be restored before returning; the
    * truncate operation must not alter the file position.
    */
 
diff --git a/fs/vfs/fs_pwrite.c b/fs/vfs/fs_pwrite.c
index 8485ca43cd..5364985f90 100644
--- a/fs/vfs/fs_pwrite.c
+++ b/fs/vfs/fs_pwrite.c
@@ -131,6 +131,12 @@ ssize_t file_pwrite(FAR struct file *filep, FAR const void *buf,
  *   end-of-file condition, or -1 on failure with errno set appropriately.
  *   See write() return values
  *
+ * Assumptions/Limitations:
+ *   POSIX requires that opening a file with the O_APPEND flag should have no
+ *   effect on the location at which pwrite() writes data.  However, on NuttX
+ *   like on Linux, if a file is opened with O_APPEND, pwrite() appends data
+ *   to the end of the file, regardless of the value of offset.
+ *
  ****************************************************************************/
 
 ssize_t pwrite(int fd, FAR const void *buf, size_t nbytes, off_t offset)