[PATCH] Re: BLKFLSBUF on ramdisks
From: Theodore Ts'o
Date: Thu May 27 2004 - 15:13:04 EST
On Wed, May 26, 2004 at 07:02:01PM -0700, Todd Poynor wrote:
> The BLKFLSBUF ioctl has a different meaning on ramdisks than on other
> block devices: the memory for the ramdisk is freed (whereas cached
> blocks are flushed to the device for most other devices, which obviously
> would be a NOP for ramdisks). At least one command, freeramdisk of
> BusyBox, expects this behavior. If certain other commands that issue
> BLKFLSBUF are inadvertently run on a ramdisk device (as in a script that
> previously tested fine on other devices) then the filesystem is
> basically corrupted instead of the normally expected result. For
> example, badblocks or e2fsck -F.
>
> While this can be initially alarming, it is easily figured out and
> avoided in the future (no one really needs to check bad blocks or
> filesystem integrity on a ramdisk, and I'd assume other uses of the
> ioctl would fall into a similar category). The two incompatible
> definitions of the ioctl do seem unfortunate, however, and I figured I'd
> ask here in case there's any interest in changing this situation; if so,
> I will gladly help, thanks,
Here's a patch (against 2.6-latest) which keeps the original BLKFLSBUF
number to perform the overloaded function, and defines a new
RAMDISKDISCARD ioctl which is reserved exclusively for discarding the
ramdisk, and a new ioctl number for BLKFLSBUF for only flushing the
buffer cache.
This keeps full binary compatibility for old applications, but it will
break source-level compatibility for programs lik BusyBox. The number
of programs that do this are extremely rare, though, so presumably
this would be acceptable.
Comments?
- Ted
===== drivers/block/ioctl.c 1.60 vs edited =====
--- 1.60/drivers/block/ioctl.c Sat May 15 02:11:56 2004
+++ edited/drivers/block/ioctl.c Thu May 27 13:10:18 2004
@@ -190,6 +190,7 @@
case BLKGETSIZE64:
return put_u64(arg, bdev->bd_inode->i_size);
case BLKFLSBUF:
+ case BLKFLSBUFOLD:
if (!capable(CAP_SYS_ADMIN))
return -EACCES;
if (disk->fops->ioctl) {
===== drivers/block/nbd.c 1.72 vs edited =====
--- 1.72/drivers/block/nbd.c Mon Feb 23 00:24:11 2004
+++ edited/drivers/block/nbd.c Thu May 27 13:10:03 2004
@@ -108,7 +108,7 @@
case NBD_SET_SIZE_BLOCKS: return "set-size-blocks";
case NBD_DISCONNECT: return "disconnect";
case BLKROSET: return "set-read-only";
- case BLKFLSBUF: return "flush-buffer-cache";
+ case BLKFLSBUFOLD: case BLKFLSBUF: return "flush-buffer-cache";
}
return "unknown";
}
===== drivers/block/rd.c 1.95 vs edited =====
--- 1.95/drivers/block/rd.c Sat May 22 04:23:01 2004
+++ edited/drivers/block/rd.c Thu May 27 13:14:07 2004
@@ -290,7 +290,7 @@
int error;
struct block_device *bdev = inode->i_bdev;
- if (cmd != BLKFLSBUF)
+ if (cmd != BLKFLSBUF && cmd != RAMDISKDISCARD)
return -ENOTTY;
/*
===== drivers/mtd/mtd_blkdevs.c 1.8 vs edited =====
--- 1.8/drivers/mtd/mtd_blkdevs.c Thu Feb 26 06:26:02 2004
+++ edited/drivers/mtd/mtd_blkdevs.c Thu May 27 13:11:30 2004
@@ -204,6 +204,7 @@
switch (cmd) {
case BLKFLSBUF:
+ case BLKFLSBUFOLD:
if (tr->flush)
return tr->flush(dev);
/* The core code did the work, we had nothing to do. */
===== include/linux/compat_ioctl.h 1.26 vs edited =====
--- 1.26/include/linux/compat_ioctl.h Tue May 25 06:39:34 2004
+++ edited/include/linux/compat_ioctl.h Thu May 27 15:41:30 2004
@@ -98,6 +98,8 @@
COMPATIBLE_IOCTL(BLKROGET)
COMPATIBLE_IOCTL(BLKRRPART)
COMPATIBLE_IOCTL(BLKFLSBUF)
+COMPATIBLE_IOCTL(BLKFLSBUFOLD)
+COMPATIBLE_IOCTL(RAMDISKCLEAR)
COMPATIBLE_IOCTL(BLKSECTSET)
COMPATIBLE_IOCTL(BLKSSZGET)
ULONG_IOCTL(BLKRASET)
===== include/linux/fs.h 1.325 vs edited =====
--- 1.325/include/linux/fs.h Tue May 25 05:53:04 2004
+++ edited/include/linux/fs.h Thu May 27 13:14:01 2004
@@ -182,7 +182,7 @@
#define BLKROGET _IO(0x12,94) /* get read-only status (0 = read_write) */
#define BLKRRPART _IO(0x12,95) /* re-read partition table */
#define BLKGETSIZE _IO(0x12,96) /* return device size /512 (long *arg) */
-#define BLKFLSBUF _IO(0x12,97) /* flush buffer cache */
+#define BLKFLSBUFOLD _IO(0x12,97) /* flush buffer cache */
#define BLKRASET _IO(0x12,98) /* set read ahead for block device */
#define BLKRAGET _IO(0x12,99) /* get current read ahead setting */
#define BLKFRASET _IO(0x12,100)/* set filesystem (mm/filemap.c) read-ahead */
@@ -204,6 +204,8 @@
#define BLKBSZGET _IOR(0x12,112,size_t)
#define BLKBSZSET _IOW(0x12,113,size_t)
#define BLKGETSIZE64 _IOR(0x12,114,size_t) /* return device size in bytes (u64 *arg) */
+#define RAMDISKDISCARD _IO(0x12,115) /* Discard ramdisk */
+#define BLKFLSBUF _IO(0x12,116) /* flush buffer cache */
#define BMAP_IOCTL 1 /* obsolete - kept for compatibility */
#define FIBMAP _IO(0x00,1) /* bmap access */
===== init/do_mounts_initrd.c 1.7 vs edited =====
--- 1.7/init/do_mounts_initrd.c Sat Mar 13 20:57:41 2004
+++ edited/init/do_mounts_initrd.c Thu May 27 13:14:18 2004
@@ -93,7 +93,7 @@
if (fd < 0) {
error = fd;
} else {
- error = sys_ioctl(fd, BLKFLSBUF, 0);
+ error = sys_ioctl(fd, RAMDISKDISCARD, 0);
sys_close(fd);
}
printk(!error ? "okay\n" : "failed\n");
-
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