user/libc: fextflags, add nonbuffering mode for fread

useful for e.g. `hexdump -r /kdev/eth` to see packets as they come in

3 files changed, 20 insertions, 7 deletions

diff --git a/src/user/lib/file.c b/src/user/lib/file.c
index c8acbfb..f2b74b1 100644
--- a/src/user/lib/file.c
+++ b/src/user/lib/file.c
@@ -87,10 +87,11 @@ FILE *fdopen(int fd, const char *mode) {
 	FILE *f;
 	f = malloc(sizeof *f);
 	if (!f) return NULL;
+	f->fd = fd;
 	f->pos = mode[0] == 'a' ? -1 : 0;
 	f->eof = false;
-	f->fd = fd;
 	f->error = false;
+	f->extflags = 0;
 	return f;
 }
 
@@ -110,6 +111,12 @@ FILE *file_clone(const FILE *f, const char *mode) {
 	return f2;
 }
 
+int fextflags(FILE *f, int extflags) {
+	int old = f->extflags;
+	f->extflags = extflags;
+	return old;
+}
+
 static void fadvance(long amt, FILE *f) {
 	bool pos_neg = f->pos < 0;
 	f->pos += amt;
@@ -133,16 +140,16 @@ size_t fread(void *restrict ptr, size_t size, size_t nitems, FILE *restrict f) {
 		if (res < 0) {
 			f->error = true;
 			errno = -res;
-			return pos/size;
+			break;
 		} else if (res == 0) {
 			f->eof = true;
-			return pos/size;
-		} else {
-			pos += res;
-			fadvance(res, f);
+			break;
 		}
+		pos += res;
+		fadvance(res, f);
+		if (f->extflags & FEXT_NOFILL) break;
 	}
-	return nitems;
+	return pos == total ? nitems : (pos/size);
 }
 
 size_t fwrite(const void *restrict ptr, size_t size, size_t nitems, FILE *restrict f) {
diff --git a/src/user/lib/file.h b/src/user/lib/file.h
index 8652566..604b070 100644
--- a/src/user/lib/file.h
+++ b/src/user/lib/file.h
@@ -6,4 +6,5 @@ struct _LIBC_FILE {
 	long pos;
 	bool eof;
 	bool error;
+	int extflags;
 };
diff --git a/src/user/lib/include/stdio.h b/src/user/lib/include/stdio.h
index 4d9cf94..b0d34a7 100644
--- a/src/user/lib/include/stdio.h
+++ b/src/user/lib/include/stdio.h
@@ -9,6 +9,10 @@
 #define SEEK_CUR 2
 #define SEEK_END 3
 
+/* stop fread() from trying to fill the entire buffer before returning
+ * i.e. it will call _syscall_read() exactly once */
+#define FEXT_NOFILL 1
+
 int printf(const char *restrict fmt, ...);
 int fprintf(FILE *restrict f, const char *restrict fmt, ...);
 
@@ -24,6 +28,7 @@ FILE *fopen(const char *path, const char *mode);
 FILE *freopen(const char *path, const char *mode, FILE *);
 FILE *fdopen(int fd, const char *mode);
 FILE *file_clone(const FILE *, const char *mode);
+int fextflags(FILE *, int extflags);
 int fclose(FILE *);
 int fflush(FILE *f);