Commit 48265250 authored by Eric Farman's avatar Eric Farman Committed by Paolo Bonzini
Browse files

block: Fix target variable of BLKSECTGET ioctl 



Commit 6f607174 ("raw-posix: Fetch max sectors for host block device")
introduced a routine to call the kernel BLKSECTGET ioctl, which stores the
result back to user space.  However, the size of the data returned depends
on the routine handling the ioctl.  The (compat_)blkdev_ioctl returns a
short, while sg_ioctl returns an int.  Thus, on big-endian systems, we can
find ourselves accidentally shifting the result to a much larger value.
(On s390x, a short is 16 bits while an int is 32 bits.)

Also, the two ioctl handlers return values in different scales (block
returns sectors, while sg returns bytes), so some tweaking of the outputs
is required such that hdev_get_max_transfer_length returns a value in a
consistent set of units.

Signed-off-by: default avatarEric Farman <farman@linux.vnet.ibm.com>
Message-Id: <20170120162527.66075-3-farman@linux.vnet.ibm.com>
Reviewed-by: default avatarFam Zheng <famz@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 2e144aa7

block/file-posix.c

+10 −7
Original line number Diff line number Diff line
@@ -651,12 +651,15 @@ static void raw_reopen_abort(BDRVReopenState *state) 
    state->opaque = NULL;

}



static int hdev_get_max_transfer_length(int fd)

static int hdev_get_max_transfer_length(BlockDriverState *bs, int fd)

{

#ifdef BLKSECTGET

    int max_sectors = 0;

    if (ioctl(fd, BLKSECTGET, &max_sectors) == 0) {

        return max_sectors;

    int max_bytes = 0;

    short max_sectors = 0;

    if (bs->sg && ioctl(fd, BLKSECTGET, &max_bytes) == 0) {

        return max_bytes;

    } else if (!bs->sg && ioctl(fd, BLKSECTGET, &max_sectors) == 0) {

        return max_sectors << BDRV_SECTOR_BITS;

    } else {

        return -errno;

    }
@@ -672,9 +675,9 @@ static void raw_refresh_limits(BlockDriverState *bs, Error **errp) 


    if (!fstat(s->fd, &st)) {

        if (S_ISBLK(st.st_mode)) {

            int ret = hdev_get_max_transfer_length(s->fd);

            if (ret > 0 && ret <= BDRV_REQUEST_MAX_SECTORS) {

                bs->bl.max_transfer = pow2floor(ret << BDRV_SECTOR_BITS);

            int ret = hdev_get_max_transfer_length(bs, s->fd);

            if (ret > 0 && ret <= BDRV_REQUEST_MAX_BYTES) {

                bs->bl.max_transfer = pow2floor(ret);

            }

        }

    }

include/block/block.h

+1 −0
Original line number Diff line number Diff line
@@ -116,6 +116,7 @@ typedef struct HDGeometry { 


#define BDRV_REQUEST_MAX_SECTORS MIN(SIZE_MAX >> BDRV_SECTOR_BITS, \

                                     INT_MAX >> BDRV_SECTOR_BITS)

#define BDRV_REQUEST_MAX_BYTES (BDRV_REQUEST_MAX_SECTORS << BDRV_SECTOR_BITS)



/*

 * Allocation status flags