casaroli commented on code in PR #20460:
URL: https://github.com/apache/nuttx/pull/20460#discussion_r4392213399
##########
fs/procfs/fs_procfsutil.c:
##########
@@ -45,6 +51,114 @@
#define LINEBUF_SIZE 128
+#if defined(CONFIG_FS_LARGEFILE)
+# define OFF_MAX INT64_MAX
+#else
+# define OFF_MAX INT32_MAX
+#endif
+
+/****************************************************************************
+ * Private Types
+ ****************************************************************************/
+
+/* Private windowed output stream state used by procfs_format_read(). */
+
+struct procfs_format_stream_s
+{
+ struct lib_outstream_s common; /* Common stream state; nput is the logical
+ * count of all bytes offered so far */
+ FAR char *buffer; /* User receive buffer */
+ size_t buflen; /* Representable copy capacity of buffer */
+ size_t copied; /* Bytes copied to buffer so far */
+ off_t skip; /* Bytes still to skip before the window */
+ int err; /* First sticky negative errno, or zero */
+};
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: procfs_format_puts
+ *
+ * Description:
+ * Consume one renderer output block through the window: bytes before the
+ * requested file position reduce the remaining skip, bytes intersecting
+ * the user buffer are copied, and bytes beyond it are discarded. A block
+ * whose length cannot be represented in the logical count records a
+ * sticky deferred -EOVERFLOW.
+ *
+ ****************************************************************************/
+
+static ssize_t procfs_format_puts(FAR struct lib_outstream_s *self,
+ FAR const void *buf, size_t len)
+{
+ FAR struct procfs_format_stream_s *stream =
+ (FAR struct procfs_format_stream_s *)self;
+ FAR const char *src = buf;
+ size_t chunk;
+
+ if (stream->err < 0 || len == 0)
+ {
+ return len;
+ }
+
+ /* Reject a block whose length cannot be represented in the logical count
+ * before it changes the count or the buffer.
+ */
+
+ if (len > OFF_MAX - stream->common.nput)
+ {
+ stream->err = -EOVERFLOW;
+ return len;
+ }
+
+ stream->common.nput += len;
+
+ /* Region 1: bytes before the requested file position */
+
+ if (stream->skip > 0)
+ {
+ if (len <= stream->skip)
+ {
+ stream->skip -= len;
+ return len;
+ }
+
+ len -= stream->skip;
+ src += stream->skip;
+ stream->skip = 0;
+ }
+
+ /* Region 2: bytes intersecting the user buffer */
+
+ chunk = MIN(len, stream->buflen - stream->copied);
+
+ if (chunk > 0)
+ {
+ memcpy(stream->buffer + stream->copied, src, chunk);
+ stream->copied += chunk;
+ }
+
+ /* Region 3: bytes beyond the buffer are discarded. The read entry point
+ * already clamped buflen so the copied count and advanced file position
+ * stay representable, so no per-byte overflow check is needed here.
+ */
+
+ return len;
Review Comment:
After a partial skip, `len` is only the rest of the block, so the function
returns fewer bytes than it consumed and a buffered stream sees a short write.
Fix: save the length at entry and return it on every path.
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