Create a fake geometry (16 heads, 64 sectors) when dealing with

a plain file and a geometry is not explicitly supplied through
command line or disktab entry.

This way you can a FAT image on a file as simply as this:

	newfs_msdos ./some/file

(right now you need a much longer command

	newfs_msdos -h 32 -u 64 -S 512 -s $total_blocks -o 0 ./some/file

Will be merged after 7.1 and 6.4 are released.
See also the related PR which suggests a similar change.

PR:		bin/121182
MFC after:	4 weeks

1 files changed, 14 insertions, 3 deletions

diff --git a/sbin/newfs_msdos/newfs_msdos.c b/sbin/newfs_msdos/newfs_msdos.c
index 1c23b24..a29448c 100644
--- a/sbin/newfs_msdos/newfs_msdos.c
+++ b/sbin/newfs_msdos/newfs_msdos.c
@@ -725,9 +725,20 @@ getdiskinfo(int fd, const char *fname, const char *dtype, __unused int oflag,
 
     /* Maybe it's a floppy drive */
     if (lp == NULL) {
-	if (ioctl(fd, DIOCGMEDIASIZE, &ms) == -1)
-	    errx(1, "Cannot get disk size, %s", strerror(errno));
-	if (ioctl(fd, FD_GTYPE, &type) != -1) {
+	if (ioctl(fd, DIOCGMEDIASIZE, &ms) == -1) {
+	    struct stat st;
+
+	    bzero(&st, sizeof(st));
+	    if (fstat(fd, &st))
+		err(1, "Cannot get disk size");
+	    /* create a fake geometry for a file image */
+	    ms = st.st_size;
+	    dlp.d_secsize = 512;
+	    dlp.d_nsectors = 64;
+	    dlp.d_ntracks = 32;
+	    dlp.d_secperunit = ms / dlp.d_secsize;
+	    lp = &dlp;
+	} else if (ioctl(fd, FD_GTYPE, &type) != -1) {
 	    dlp.d_secsize = 128 << type.secsize;
 	    dlp.d_nsectors = type.sectrac;
 	    dlp.d_ntracks = type.heads;