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Posted to commits@nuttx.apache.org by GitBox <gi...@apache.org> on 2022/10/18 10:26:52 UTC
[GitHub] [incubator-nuttx] fjpanag opened a new pull request, #7345: Added flush of the read buffers when a file is reopened.
fjpanag opened a new pull request, #7345:
URL: https://github.com/apache/incubator-nuttx/pull/7345
## Summary
When `CONFIG_STDIO_DISABLE_BUFFERING` is not set (i.e. buffering IS enabled), and when a file is reopened (`freopen()`), then the read buffers where not flushed.
This had as a result that the file position and the buffer became de-synchronized.
When reading from this file, wrong data were returned, from a position different to what the file position dictated.
The addition of the `fseek()` call ensures that the file position is correctly set to what the re-open wants, and internally calls `lib_rdflush()`.
## Impact
Bug fix.
## Testing
Tested on simulator with a test scenario that:
1. Opened an existing file, and read 1 character from it.
2. Re-opened the file.
3. Read 1 character from the file again.
Before, step 3 returned the *second* character of the file.
Now it correctly returns the *first* character, as it should.
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[GitHub] [incubator-nuttx] xiaoxiang781216 commented on a diff in pull request #7345: Added flush of the read buffers when a file is reopened.
Posted by GitBox <gi...@apache.org>.
xiaoxiang781216 commented on code in PR #7345:
URL: https://github.com/apache/incubator-nuttx/pull/7345#discussion_r998032941
##########
libs/libc/stdio/lib_freopen.c:
##########
@@ -74,6 +75,7 @@ FAR FILE *freopen(FAR const char *path, FAR const char *mode,
int oflags;
int ret;
int fd;
+ off_t f_pos;
Review Comment:
```suggestion
off_t pos;
```
##########
libs/libc/stdio/lib_freopen.c:
##########
@@ -100,9 +102,19 @@ FAR FILE *freopen(FAR const char *path, FAR const char *mode,
return NULL;
}
- /* Flush the stream and duplicate the new fd to it */
+ /* Get the new file position */
+
+ f_pos = lseek(fd, 0, SEEK_CUR);
+
+ /* Flush the stream and set the file position. The later is needed to
+ * ensure that the read buffers are also flushed.
+ */
fflush(stream);
+ fseek(stream, f_pos, SEEK_SET);
Review Comment:
should we add a new function to simply discard the buffer?
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[GitHub] [incubator-nuttx] xiaoxiang781216 merged pull request #7345: Added flush of the read buffers when a file is reopened.
Posted by GitBox <gi...@apache.org>.
xiaoxiang781216 merged PR #7345:
URL: https://github.com/apache/incubator-nuttx/pull/7345
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[GitHub] [incubator-nuttx] fjpanag commented on a diff in pull request #7345: Added flush of the read buffers when a file is reopened.
Posted by GitBox <gi...@apache.org>.
fjpanag commented on code in PR #7345:
URL: https://github.com/apache/incubator-nuttx/pull/7345#discussion_r998091652
##########
libs/libc/stdio/lib_freopen.c:
##########
@@ -100,9 +102,19 @@ FAR FILE *freopen(FAR const char *path, FAR const char *mode,
return NULL;
}
- /* Flush the stream and duplicate the new fd to it */
+ /* Get the new file position */
+
+ f_pos = lseek(fd, 0, SEEK_CUR);
+
+ /* Flush the stream and set the file position. The later is needed to
+ * ensure that the read buffers are also flushed.
+ */
fflush(stream);
+ fseek(stream, f_pos, SEEK_SET);
Review Comment:
I will change it to directly call `lib_rdflush()`.
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