POSIX: lseek: support SEEK_DATA and SEEK_HOLE constants

this is queued for issue 8: https://www.austingroupbugs.net/view.php?id=415
this implementation calls the ioctl hook of the filesystem with BSD-like constants
FIOSEEKDATA and FIOSEEKHOLE. if the hook doesn't know the constants, we use the stat size
to return the last hole (as proposed in the draft spec).

Change-Id: I5d052eed87e29b70491a7ff534e244896469d03e
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3385
Reviewed-by: Jérôme Duval <[email protected]>

headers/posix/sys/ioctl.h

@@ -12,4 +12,7 @@
 #define FIONBIO 	0xbe000000
 #define FIONREAD	0xbe000001
 
+#define FIOSEEKDATA	0xbe000002
+#define FIOSEEKHOLE	0xbe000003
+
 #endif	/* _SYS_IOCTL_H */

headers/posix/unistd.h

@@ -151,6 +151,12 @@
 #ifndef SEEK_END
 #	define SEEK_END 2
 #endif
+#ifndef SEEK_DATA
+#	define SEEK_DATA 3
+#endif
+#ifndef SEEK_HOLE
+#	define SEEK_HOLE 4
+#endif
 
 
 #ifdef __cplusplus

src/system/kernel/fs/vfs.cpp

@@ -18,6 +18,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <sys/file.h>
+#include <sys/ioctl.h>
 #include <sys/resource.h>
 #include <sys/stat.h>
 #include <unistd.h>
@@ -5858,6 +5859,39 @@ file_seek(struct file_descriptor* descriptor, off_t pos, int seekType)
 
 			break;
 		}
+		case SEEK_DATA:
+		case SEEK_HOLE:
+		{
+			status_t status = B_BAD_VALUE;
+			if (HAS_FS_CALL(vnode, ioctl)) {
+				offset = pos;
+				status = FS_CALL(vnode, ioctl, descriptor->cookie,
+					seekType == SEEK_DATA ? FIOSEEKDATA : FIOSEEKHOLE,
+					&offset, sizeof(offset));
+				if (status == B_OK) {
+					if (offset > pos)
+						offset -= pos;
+					break;
+				}
+			}
+			if (status != B_BAD_VALUE && status != B_DEV_INVALID_IOCTL)
+				return status;
+
+			// basic implementation with stat() the node
+			if (!HAS_FS_CALL(vnode, read_stat) || isDevice)
+				return B_BAD_VALUE;
+
+			struct stat stat;
+			status = FS_CALL(vnode, read_stat, &stat);
+			if (status != B_OK)
+				return status;
+
+			off_t end = stat.st_size;
+			if (pos >= end)
+				return ENXIO;
+			offset = seekType == SEEK_HOLE ? end - pos : 0;
+			break;
+		}
 		default:
 			return B_BAD_VALUE;
 	}