[syslinux] [PATCH 1/3] COMBOOT API: Improve readdir

[Gene Cumm]

From: Gene Cumm <gene.cumm at gmail.com>

COMBOOT API: Improve readdir.  Now returns C struct stat st_mode
compatible data in DX rather than the raw data from a FAT filesystem
or C struct dirent d_mode compatible data.

Signed-off-by: Gene Cumm <gene.cumm at gmail.com>

---

If I return something that's compatible with the C struct stat st_mode
member, this can be used for more that just determining the type of
file.  It might be forseeable that something else in st_mode may prove
useful.  My reasoning is that I can change the COMBOOT API now before
it's in a release but changing after release (and looking like 3.74,
right now) should probably be avoided at all costs (preferably, it's
cast in stone).  I may, down the road, look at how to return a date in
another register but I also see that as acceptable as it doesn't
change existing behavior, thereby breaking existing code.


diff --git a/core/comboot.inc b/core/comboot.inc
index 2ff5f33..bab3d6a 100644
--- a/core/comboot.inc
+++ b/core/comboot.inc
@@ -1092,7 +1092,7 @@ comapi_readdir:
 		mov si,P_SI
 		call readdir
 		mov P_EAX,eax
-		mov P_DL,dl
+		mov P_DX,dx
 		mov P_EBX,ebx
 		mov P_SI,si
 		ret
diff --git a/core/ldlinux.asm b/core/ldlinux.asm
index a24f396..bb5bf14 100644
--- a/core/ldlinux.asm
+++ b/core/ldlinux.asm
@@ -1377,6 +1377,40 @@ searchdir:
 		ret

 ;
+; fatattr_to_st_mode: Translate a FAT attribute to struct stat st_mode.
+;
+;	DL	FAT Attribute
+;
+;	Returns st_mode
+;	DX	st_mode
+;
+
+fatattr_to_st_mode:
+		push eax
+		test dl,0xC8	; 0x80 Unknown	0x40 Device(Internal)
+				;	0x08 Label
+		jnz .zero
+		mov ax,0444o
+		test dl,1	; 1 ReadOnly
+		jnz .is_ro
+		add ax,0222o
+.is_ro:
+		test dl,0x10	; 0x10 Directory
+		jz .not_dir
+		add ax,040111o	; Dir and Execute
+		jmp .done
+.not_dir:
+		add ax,0100000o	; Regular file
+.done:
+		mov dx,ax
+		jmp .end
+.zero:		; Any condition that will result in an all zero return
+		mov dx,0
+.end:
+		pop eax
+		ret
+
+;
 ; readdir: Read one file from a directory
 ;
 ;	ES:DI	-> String buffer (filename)
@@ -1550,6 +1584,7 @@ readdir:
 .get_info:
 		mov ebx,[gs:si+28]	; length
 		mov dl,[gs:si+11]	; type
+		call fatattr_to_st_mode
 .next_entry:
 		add si,DIRENT_SIZE
 		dec cx
diff --git a/doc/comboot.txt b/doc/comboot.txt
index 5f57da7..135a5bc 100644
--- a/doc/comboot.txt
+++ b/doc/comboot.txt
@@ -947,16 +947,17 @@ AX=0021h [3.74] Read directory
 	Input:	AX	0020h
 		SI	directory handle
 		ES:DI	buffer for file name
-	Output:	DL	Type of file
+	Output:	DX	Mode of file
 		SI	directory handle, or 0 if end of directory was reached
 		EAX	Size of file
 		EBX	Inode of file

 	Read one filename from the directory, incrementing the
 	directory structure at SI as appropriate, storing the filename
-	into the buffer at ES:DI, and returning the type of the file
-	in DL, the file length in EAX, the inode/file number in EBX
-	and the updated directory handle.
+	into the buffer at ES:DI, and returning the mode of the file
+	in DX, the file length in EAX, the inode/file number in EBX
+	and the updated directory handle.  The mode in DX is compatible
+	with the struct stat st_mode member.


 AX=0022h [3.74] Close directory