From: Stephen Kitt > Sent: 09 March 2018 22:34 > > COMMAND_SIZE currently uses an array of values in block/scsi_ioctl.c. > A number of device_handler functions use this to initialise arrays, > and this is flagged by -Wvla. > > This patch replaces COMMAND_SIZE with a variant using a formula which > can be resolved at compile time in cases where the opcode is fixed, > resolving the array size and avoiding the VLA. The downside is that > the code is less maintainable and that some call sites end up having > more complex generated code. > > Since scsi_command_size_tbl is dropped, we can remove the dependency > on BLK_SCSI_REQUEST from drivers/target/Kconfig. > > This was prompted by https://lkml.org/lkml/2018/3/7/621 > > Signed-off-by: Stephen Kitt <steve@xxxxxxx> > --- > block/scsi_ioctl.c | 8 -------- > drivers/target/Kconfig | 1 - > include/scsi/scsi_common.h | 13 +++++++++++-- > 3 files changed, 11 insertions(+), 11 deletions(-) > > diff --git a/block/scsi_ioctl.c b/block/scsi_ioctl.c > index 60b471f8621b..b9e176e537be 100644 > --- a/block/scsi_ioctl.c > +++ b/block/scsi_ioctl.c > @@ -41,14 +41,6 @@ struct blk_cmd_filter { > > static struct blk_cmd_filter blk_default_cmd_filter; > > -/* Command group 3 is reserved and should never be used. */ > -const unsigned char scsi_command_size_tbl[8] = > -{ > - 6, 10, 10, 12, > - 16, 12, 10, 10 > -}; > -EXPORT_SYMBOL(scsi_command_size_tbl); > - > #include <scsi/sg.h> > > static int sg_get_version(int __user *p) > diff --git a/drivers/target/Kconfig b/drivers/target/Kconfig > index 4c44d7bed01a..b5f05b60cf06 100644 > --- a/drivers/target/Kconfig > +++ b/drivers/target/Kconfig > @@ -4,7 +4,6 @@ menuconfig TARGET_CORE > depends on SCSI && BLOCK > select CONFIGFS_FS > select CRC_T10DIF > - select BLK_SCSI_REQUEST # only for scsi_command_size_tbl.. > select SGL_ALLOC > default n > help > diff --git a/include/scsi/scsi_common.h b/include/scsi/scsi_common.h > index 731ac09ed231..48d950666376 100644 > --- a/include/scsi/scsi_common.h > +++ b/include/scsi/scsi_common.h > @@ -15,8 +15,17 @@ scsi_varlen_cdb_length(const void *hdr) > return ((struct scsi_varlen_cdb_hdr *)hdr)->additional_cdb_length + 8; > } > > -extern const unsigned char scsi_command_size_tbl[8]; > -#define COMMAND_SIZE(opcode) scsi_command_size_tbl[((opcode) >> 5) & 7] > +/* > + * SCSI command sizes are as follows, in bytes, for fixed size commands, per > + * group: 6, 10, 10, 12, 16, 12, 10, 10. The top three bits of an opcode > + * determine its group. > + * The size table is encoded into a 32-bit value by subtracting each value > + * from 16, resulting in a value of 1715488362 > + * (6 << 28 + 6 << 24 + 4 << 20 + 0 << 16 + 4 << 12 + 6 << 8 + 6 << 4 + 10). > + * Command group 3 is reserved and should never be used. > + */ > +#define COMMAND_SIZE(opcode) \ > + (16 - (15 & (1715488362 >> (4 * (((opcode) >> 5) & 7))))) Why not: (6 + (15 & (0x446a6440u .... Specifying the constant in hex makes it more obvious. It is a shame about the 16, but an offset is easier than the negate. David
