[v21,30/46] sg: expand sg_comm_wr_t

Message ID	20211003163151.585349-31-dgilbert@interlog.com (mailing list archive)
State	Deferred
Headers	show Return-Path: <linux-scsi-owner@kernel.org> From: Douglas Gilbert <dgilbert@interlog.com> To: linux-scsi@vger.kernel.org Cc: martin.petersen@oracle.com, jejb@linux.vnet.ibm.com, hare@suse.de, Damien.LeMoal@wdc.com, Hannes Reinecke <hare@suse.com> Subject: [PATCH v21 30/46] sg: expand sg_comm_wr_t Date: Sun, 3 Oct 2021 12:31:35 -0400 Message-Id: <20211003163151.585349-31-dgilbert@interlog.com> In-Reply-To: <20211003163151.585349-1-dgilbert@interlog.com> References: <20211003163151.585349-1-dgilbert@interlog.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk
Series	sg: add v4 interface \| expand [v21,00/46] sg: add v4 interface [v21,01/46] sg: move functions around [v21,02/46] sg: remove typedefs, type+formatting cleanup [v21,03/46] sg: sg_log and is_enabled [v21,04/46] sg: rework sg_poll(), minor changes [v21,05/46] sg: bitops in sg_device [v21,06/46] sg: make open count an atomic [v21,07/46] sg: move header to uapi section [v21,08/46] sg: speed sg_poll and sg_get_num_waiting [v21,09/46] sg: sg_allow_if_err_recovery and renames [v21,10/46] sg: improve naming [v21,11/46] sg: change rwlock to spinlock [v21,12/46] sg: ioctl handling [v21,13/46] sg: split sg_read [v21,14/46] sg: sg_common_write add structure for arguments [v21,15/46] sg: rework sg_vma_fault [v21,16/46] sg: rework sg_mmap [v21,17/46] sg: replace sg_allow_access [v21,18/46] sg: rework scatter gather handling [v21,19/46] sg: introduce request state machine [v21,20/46] sg: sg_find_srp_by_id [v21,21/46] sg: sg_fill_request_element [v21,22/46] sg: printk change %p to %pK [v21,23/46] sg: xarray for fds in device [v21,24/46] sg: xarray for reqs in fd [v21,25/46] sg: replace rq array with xarray [v21,26/46] sg: sense buffer rework [v21,27/46] sg: add sg v4 interface support [v21,28/46] sg: rework debug info [v21,29/46] sg: add 8 byte SCSI LUN to sg_scsi_id [v21,30/46] sg: expand sg_comm_wr_t [v21,31/46] sg: add sg_iosubmit_v3 and sg_ioreceive_v3 ioctls [v21,32/46] sg: add some __must_hold macros [v21,33/46] sg: move procfs objects to avoid forward decls [v21,34/46] sg: protect multiple receivers [v21,35/46] sg: first debugfs support [v21,36/46] sg: rework mmap support [v21,37/46] sg: defang allow_dio [v21,38/46] sg: warn v3 write system call users [v21,39/46] sg: add mmap_sz tracking [v21,40/46] sg: remove rcv_done request state [v21,41/46] sg: track lowest inactive and await indexes [v21,42/46] sg: remove unit attention check for device changed [v21,43/46] sg: no_dxfer: move to/from kernel buffers [v21,44/46] sg: add blk_poll support [v21,45/46] sg: add statistics similar to st [v21,46/46] sg: bump version to 4.0.12

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c index d7d52c0de9f9..e9a91b012429 100644 --- a/drivers/scsi/sg.c +++ b/drivers/scsi/sg.c @@ -252,36 +252,38 @@ struct sg_device { /* holds the state of each scsi generic device */ struct sg_comm_wr_t { /* arguments to sg_common_write() */ int timeout; + int cmd_len; unsigned long frq_bm[1]; /* see SG_FRQ_* defines above */ union { /* selector is frq_bm.SG_FRQ_IS_V4I */ struct sg_io_hdr *h3p; struct sg_io_v4 *h4p; }; - u8 *cmnd; + struct sg_fd *sfp; + struct file *filp; + const u8 __user *u_cmdp; }; /* tasklet or soft irq callback */ static void sg_rq_end_io(struct request *rq, blk_status_t status); /* Declarations of other static functions used before they are defined */ static int sg_proc_init(void); -static int sg_start_req(struct sg_request *srp, u8 *cmd, int cmd_len, - struct sg_io_v4 *h4p, int dxfer_dir); +static int sg_start_req(struct sg_request *srp, struct sg_comm_wr_t *cwrp, + int dxfer_dir); static void sg_finish_scsi_blk_rq(struct sg_request *srp); static int sg_mk_sgat(struct sg_scatter_hold *schp, struct sg_fd *sfp, int minlen); static void sg_remove_sgat_helper(struct sg_fd *sfp, struct sg_scatter_hold *schp); static int sg_v3_submit(struct file *filp, struct sg_fd *sfp, struct sg_io_hdr *hp, bool sync, struct sg_request **o_srp); -static struct sg_request *sg_common_write(struct sg_fd *sfp, - struct sg_comm_wr_t *cwrp); +static struct sg_request *sg_common_write(struct sg_comm_wr_t *cwrp); static int sg_read_append(struct sg_request *srp, void __user *outp, int num_xfer); static void sg_remove_sgat(struct sg_request *srp); static struct sg_fd *sg_add_sfp(struct sg_device *sdp); static void sg_remove_sfp(struct kref *); static struct sg_request *sg_find_srp_by_id(struct sg_fd *sfp, int id); -static struct sg_request *sg_setup_req(struct sg_fd *sfp, int dxfr_len, - struct sg_comm_wr_t *cwrp); +static struct sg_request *sg_setup_req(struct sg_comm_wr_t *cwrp, + int dxfr_len); static void sg_deact_request(struct sg_fd *sfp, struct sg_request *srp); static struct sg_device *sg_get_dev(int min_dev); static void sg_device_destroy(struct kref *kref); @@ -572,7 +574,6 @@ sg_write(struct file *filp, const char __user *p, size_t count, loff_t *ppos) struct sg_device *sdp; struct sg_fd *sfp; struct sg_request *srp; - u8 cmnd[SG_MAX_CDB_SIZE]; struct sg_header ov2hdr; struct sg_io_hdr v3hdr; struct sg_header *ohp = &ov2hdr; @@ -684,9 +685,6 @@ sg_write(struct file *filp, const char __user *p, size_t count, loff_t *ppos) h3p->flags = input_size; /* structure abuse ... */ h3p->pack_id = ohp->pack_id; h3p->usr_ptr = NULL; - cmnd[0] = opcode; - if (copy_from_user(cmnd + 1, p + 1, cmd_size - 1)) - return -EFAULT; /* * SG_DXFER_TO_FROM_DEV is functionally equivalent to SG_DXFER_FROM_DEV, * but it is possible that the app intended SG_DXFER_TO_DEV, because @@ -698,13 +696,16 @@ sg_write(struct file *filp, const char __user *p, size_t count, loff_t *ppos) "%s: data in/out %d/%d bytes for SCSI command 0x%x-- guessing data in;\n" " program %s not setting count and/or reply_len properly\n", __func__, ohp->reply_len - (int)SZ_SG_HEADER, - input_size, (unsigned int)cmnd[0], current->comm); + input_size, (unsigned int)opcode, current->comm); } - cwr.frq_bm[0] = 0; /* initial state clear for all req flags */ cwr.h3p = h3p; + cwr.frq_bm[0] = 0; cwr.timeout = sfp->timeout; - cwr.cmnd = cmnd; - srp = sg_common_write(sfp, &cwr); + cwr.cmd_len = cmd_size; + cwr.filp = filp; + cwr.sfp = sfp; + cwr.u_cmdp = p; + srp = sg_common_write(&cwr); return (IS_ERR(srp)) ? PTR_ERR(srp) : (int)count; } @@ -746,31 +747,29 @@ static int sg_v3_submit(struct file *filp, struct sg_fd *sfp, struct sg_io_hdr *hp, bool sync, struct sg_request **o_srp) { - int res, timeout; unsigned long ul_timeout; struct sg_request *srp; struct sg_comm_wr_t cwr; - u8 cmnd[SG_MAX_CDB_SIZE]; /* now doing v3 blocking (sync) or non-blocking submission */ if (hp->flags & SG_FLAG_MMAP_IO) { - res = sg_chk_mmap(sfp, hp->flags, hp->dxfer_len); + int res = sg_chk_mmap(sfp, hp->flags, hp->dxfer_len); + if (res) return res; } /* when v3 seen, allow cmd_q on this fd (def: no cmd_q) */ set_bit(SG_FFD_CMD_Q, sfp->ffd_bm); ul_timeout = msecs_to_jiffies(hp->timeout); - timeout = min_t(unsigned long, ul_timeout, INT_MAX); - res = sg_fetch_cmnd(filp, sfp, hp->cmdp, hp->cmd_len, cmnd); - if (res) - return res; cwr.frq_bm[0] = 0; __assign_bit(SG_FRQ_SYNC_INVOC, cwr.frq_bm, (int)sync); cwr.h3p = hp; - cwr.timeout = timeout; - cwr.cmnd = cmnd; - srp = sg_common_write(sfp, &cwr); + cwr.timeout = min_t(unsigned long, ul_timeout, INT_MAX); + cwr.cmd_len = hp->cmd_len; + cwr.filp = filp; + cwr.sfp = sfp; + cwr.u_cmdp = hp->cmdp; + srp = sg_common_write(&cwr); if (IS_ERR(srp)) return PTR_ERR(srp); if (o_srp) @@ -782,11 +781,10 @@ static int sg_submit_v4(struct file *filp, struct sg_fd *sfp, void __user *p, struct sg_io_v4 *h4p, bool sync, struct sg_request **o_srp) { - int timeout, res; + int res = 0; unsigned long ul_timeout; struct sg_request *srp; struct sg_comm_wr_t cwr; - u8 cmnd[SG_MAX_CDB_SIZE]; if (h4p->flags & SG_FLAG_MMAP_IO) { int len = 0; @@ -802,18 +800,16 @@ sg_submit_v4(struct file *filp, struct sg_fd *sfp, void __user *p, /* once v4 (or v3) seen, allow cmd_q on this fd (def: no cmd_q) */ set_bit(SG_FFD_CMD_Q, sfp->ffd_bm); ul_timeout = msecs_to_jiffies(h4p->timeout); - timeout = min_t(unsigned long, ul_timeout, INT_MAX); - res = sg_fetch_cmnd(filp, sfp, cuptr64(h4p->request), h4p->request_len, - cmnd); - if (res) - return res; + cwr.filp = filp; + cwr.sfp = sfp; cwr.frq_bm[0] = 0; - assign_bit(SG_FRQ_SYNC_INVOC, cwr.frq_bm, (int)sync); - set_bit(SG_FRQ_IS_V4I, cwr.frq_bm); + __assign_bit(SG_FRQ_SYNC_INVOC, cwr.frq_bm, (int)sync); + __set_bit(SG_FRQ_IS_V4I, cwr.frq_bm); cwr.h4p = h4p; - cwr.timeout = timeout; - cwr.cmnd = cmnd; - srp = sg_common_write(sfp, &cwr); + cwr.timeout = min_t(unsigned long, ul_timeout, INT_MAX); + cwr.cmd_len = h4p->request_len; + cwr.u_cmdp = cuptr64(h4p->request); + srp = sg_common_write(&cwr); if (IS_ERR(srp)) return PTR_ERR(srp); if (o_srp) @@ -985,13 +981,14 @@ sg_execute_cmd(struct sg_fd *sfp, struct sg_request *srp) * N.B. pack_id placed in sg_io_v4::request_extra field. */ static struct sg_request * -sg_common_write(struct sg_fd *sfp, struct sg_comm_wr_t *cwrp) +sg_common_write(struct sg_comm_wr_t *cwrp) { int res = 0; - int dxfr_len, dir, cmd_len; + int dxfr_len, dir; int pack_id = SG_PACK_ID_WILDCARD; u32 rq_flags; - struct sg_device *sdp = sfp->parentdp; + struct sg_fd *fp = cwrp->sfp; + struct sg_device *sdp = fp->parentdp; struct sg_request *srp; struct sg_io_hdr *hi_p; struct sg_io_v4 *h4p; @@ -1023,40 +1020,36 @@ sg_common_write(struct sg_fd *sfp, struct sg_comm_wr_t *cwrp) if (dxfr_len >= SZ_256M) return ERR_PTR(-EINVAL); - srp = sg_setup_req(sfp, dxfr_len, cwrp); + srp = sg_setup_req(cwrp, dxfr_len); if (IS_ERR(srp)) return srp; srp->rq_flags = rq_flags; srp->pack_id = pack_id; if (h4p) { - memset(&srp->s_hdr4, 0, sizeof(srp->s_hdr4)); srp->s_hdr4.usr_ptr = h4p->usr_ptr; srp->s_hdr4.sbp = uptr64(h4p->response); srp->s_hdr4.max_sb_len = h4p->max_response_len; srp->s_hdr4.cmd_len = h4p->request_len; srp->s_hdr4.dir = dir; - cmd_len = h4p->request_len; + srp->s_hdr4.out_resid = 0; } else { /* v3 interface active */ - cmd_len = hi_p->cmd_len; memcpy(&srp->s_hdr3, hi_p, sizeof(srp->s_hdr3)); } - srp->cmd_opcode = cwrp->cmnd[0];/* hold opcode of command for debug */ - SG_LOG(4, sfp, "%s: opcode=0x%02x, cdb_sz=%d, pack_id=%d\n", __func__, - (int)cwrp->cmnd[0], cmd_len, pack_id); - - res = sg_start_req(srp, cwrp->cmnd, cmd_len, h4p, dir); + res = sg_start_req(srp, cwrp, dir); if (res < 0) /* probably out of space --> -ENOMEM */ goto err_out; + SG_LOG(4, fp, "%s: opcode=0x%02x, cdb_sz=%d, pack_id=%d\n", __func__, + srp->cmd_opcode, cwrp->cmd_len, pack_id); if (unlikely(SG_IS_DETACHING(sdp))) { res = -ENODEV; goto err_out; } srp->rq->timeout = cwrp->timeout; - sg_execute_cmd(sfp, srp); + sg_execute_cmd(fp, srp); return srp; err_out: - sg_deact_request(sfp, srp); + sg_deact_request(fp, srp); return ERR_PTR(res); } @@ -1273,8 +1266,8 @@ sg_ctl_ioreceive(struct file *filp, struct sg_fd *sfp, void __user *p) id)); if (unlikely(SG_IS_DETACHING(sdp))) return -ENODEV; - if (res) /* -ERESTARTSYS as signal hit process */ - return res; + if (res) + return res; /* signal --> -ERESTARTSYS */ } /* now srp should be valid */ return sg_receive_v4(sfp, srp, p, h4p); } @@ -2623,7 +2616,7 @@ init_sg(void) } sg_sysfs_valid = true; rc = scsi_register_interface(&sg_interface); - if (0 == rc) { + if (rc == 0) { sg_proc_init(); return 0; } @@ -2672,11 +2665,10 @@ sg_chk_dio_allowed(struct sg_device *sdp, struct sg_request *srp, return false; } -static void +static inline void sg_set_map_data(const struct sg_scatter_hold *schp, bool up_valid, struct rq_map_data *mdp) { - memset(mdp, 0, sizeof(*mdp)); mdp->pages = schp->pages; mdp->page_order = schp->page_order; mdp->nr_entries = schp->num_sgat; @@ -2685,8 +2677,7 @@ sg_set_map_data(const struct sg_scatter_hold *schp, bool up_valid, } static int -sg_start_req(struct sg_request *srp, u8 *cmd, int cmd_len, - struct sg_io_v4 *h4p, int dxfer_dir) +sg_start_req(struct sg_request *srp, struct sg_comm_wr_t *cwrp, int dxfer_dir) { bool reserved, us_xfer; int res = 0; @@ -2696,7 +2687,7 @@ sg_start_req(struct sg_request *srp, u8 *cmd, int cmd_len, void __user *up; struct request *rq; struct scsi_request *scsi_rp; - struct sg_fd *sfp = srp->parentfp; + struct sg_fd *sfp = cwrp->sfp; struct sg_device *sdp; struct sg_scatter_hold *req_schp; struct request_queue *q; @@ -2706,20 +2697,21 @@ sg_start_req(struct sg_request *srp, u8 *cmd, int cmd_len, struct rq_map_data map_data; sdp = sfp->parentdp; - if (cmd_len > BLK_MAX_CDB) { /* for longer SCSI cdb_s */ - long_cmdp = kzalloc(cmd_len, GFP_KERNEL); + if (cwrp->cmd_len > BLK_MAX_CDB) { /* for longer SCSI cdb_s */ + long_cmdp = kzalloc(cwrp->cmd_len, GFP_KERNEL); if (!long_cmdp) return -ENOMEM; SG_LOG(5, sfp, "%s: long_cmdp=0x%pK ++\n", __func__, long_cmdp); } - if (h4p) { + if (test_bit(SG_FRQ_IS_V4I, srp->frq_bm)) { + struct sg_io_v4 *h4p = cwrp->h4p; + if (dxfer_dir == SG_DXFER_TO_DEV) { r0w = WRITE; up = uptr64(h4p->dout_xferp); dxfer_len = (int)h4p->dout_xfer_len; iov_count = h4p->dout_iovec_count; } else if (dxfer_dir == SG_DXFER_FROM_DEV) { - r0w = READ; up = uptr64(h4p->din_xferp); dxfer_len = (int)h4p->din_xfer_len; iov_count = h4p->din_iovec_count; @@ -2758,10 +2750,17 @@ sg_start_req(struct sg_request *srp, u8 *cmd, int cmd_len, scsi_rp = scsi_req(rq); srp->rq = rq; - if (cmd_len > BLK_MAX_CDB) - scsi_rp->cmd = long_cmdp; - memcpy(scsi_rp->cmd, cmd, cmd_len); - scsi_rp->cmd_len = cmd_len; + if (cwrp->cmd_len > BLK_MAX_CDB) + scsi_rp->cmd = long_cmdp; /* transfer ownership */ + if (cwrp->u_cmdp) + res = sg_fetch_cmnd(cwrp->filp, sfp, cwrp->u_cmdp, + cwrp->cmd_len, scsi_rp->cmd); + else + res = -EPROTO; + if (res) + goto fini; + scsi_rp->cmd_len = cwrp->cmd_len; + srp->cmd_opcode = scsi_rp->cmd[0]; us_xfer = !(srp->rq_flags & SG_FLAG_NO_DXFER); assign_bit(SG_FRQ_NO_US_XFER, srp->frq_bm, !us_xfer); reserved = (sfp->rsv_srp == srp); @@ -2784,7 +2783,7 @@ sg_start_req(struct sg_request *srp, u8 *cmd, int cmd_len, } if (likely(md)) { /* normal, "indirect" IO */ - if (unlikely((srp->rq_flags & SG_FLAG_MMAP_IO))) { + if (unlikely(srp->rq_flags & SG_FLAG_MMAP_IO)) { /* mmap IO must use and fit in reserve request */ if (!reserved || dxfer_len > req_schp->buflen) res = reserved ? -ENOMEM : -EBUSY; @@ -2793,7 +2792,7 @@ sg_start_req(struct sg_request *srp, u8 *cmd, int cmd_len, res = sg_mk_sgat(&srp->sgat_h, sfp, up_sz); } - if (res) + if (unlikely(res)) goto fini; sg_set_map_data(req_schp, !!up, md); @@ -3124,7 +3123,7 @@ sg_mk_srp_sgat(struct sg_fd *sfp, bool first, int db_len) return n_srp; if (db_len > 0) { res = sg_mk_sgat(&n_srp->sgat_h, sfp, db_len); - if (res) { + if (unlikely(res)) { kfree(n_srp); return ERR_PTR(res); } @@ -3177,18 +3176,18 @@ sg_build_reserve(struct sg_fd *sfp, int buflen) * failure returns a negated errno value twisted by ERR_PTR() macro. */ static struct sg_request * -sg_setup_req(struct sg_fd *sfp, int dxfr_len, struct sg_comm_wr_t *cwrp) +sg_setup_req(struct sg_comm_wr_t *cwrp, int dxfr_len) { bool act_empty = false; bool found = false; - bool mk_new_srp = false; + bool mk_new_srp = true; bool try_harder = false; - int res; int num_inactive = 0; unsigned long idx, last_idx, iflags; + struct sg_fd *fp = cwrp->sfp; struct sg_request *r_srp = NULL; /* request to return */ struct sg_request *last_srp = NULL; - struct xarray *xafp = &sfp->srp_arr; + struct xarray *xafp = &fp->srp_arr; __maybe_unused const char *cp; start_again: @@ -3241,18 +3240,19 @@ sg_setup_req(struct sg_fd *sfp, int dxfr_len, struct sg_comm_wr_t *cwrp) mk_new_srp = true; } if (mk_new_srp) { - bool allow_cmd_q = test_bit(SG_FFD_CMD_Q, sfp->ffd_bm); + bool allow_cmd_q = test_bit(SG_FFD_CMD_Q, fp->ffd_bm); + int res; u32 n_idx; struct xa_limit xal = { .max = 0, .min = 0 }; cp = "new"; - if (!allow_cmd_q && atomic_read(&sfp->submitted) > 0) { + if (!allow_cmd_q && atomic_read(&fp->submitted) > 0) { r_srp = ERR_PTR(-EDOM); - SG_LOG(6, sfp, "%s: trying 2nd req but cmd_q=false\n", + SG_LOG(6, fp, "%s: trying 2nd req but cmd_q=false\n", __func__); goto fini; } - r_srp = sg_mk_srp_sgat(sfp, act_empty, dxfr_len); + r_srp = sg_mk_srp_sgat(fp, act_empty, dxfr_len); if (IS_ERR(r_srp)) { if (!try_harder && dxfr_len < SG_DEF_SECTOR_SZ && num_inactive > 0) { @@ -3263,11 +3263,11 @@ sg_setup_req(struct sg_fd *sfp, int dxfr_len, struct sg_comm_wr_t *cwrp) } atomic_set(&r_srp->rq_st, SG_RS_BUSY); xa_lock_irqsave(xafp, iflags); - xal.max = atomic_inc_return(&sfp->req_cnt); + xal.max = atomic_inc_return(&fp->req_cnt); res = __xa_alloc(xafp, &n_idx, r_srp, xal, GFP_KERNEL); xa_unlock_irqrestore(xafp, iflags); if (res < 0) { - SG_LOG(1, sfp, "%s: xa_alloc() failed, errno=%d\n", + SG_LOG(1, fp, "%s: xa_alloc() failed, errno=%d\n", __func__, -res); sg_remove_sgat(r_srp); kfree(r_srp); @@ -3276,17 +3276,18 @@ sg_setup_req(struct sg_fd *sfp, int dxfr_len, struct sg_comm_wr_t *cwrp) } idx = n_idx; r_srp->rq_idx = idx; - r_srp->parentfp = sfp; - SG_LOG(4, sfp, "%s: mk_new_srp=0x%pK ++\n", __func__, r_srp); + r_srp->parentfp = fp; + SG_LOG(4, fp, "%s: mk_new_srp=0x%pK ++\n", __func__, r_srp); } r_srp->frq_bm[0] = cwrp->frq_bm[0]; /* assumes <= 32 req flags */ r_srp->sgat_h.dlen = dxfr_len;/* must be <= r_srp->sgat_h.buflen */ r_srp->cmd_opcode = 0xff; /* set invalid opcode (VS), 0x0 is TUR */ fini: if (IS_ERR(r_srp)) - SG_LOG(1, sfp, "%s: err=%ld\n", __func__, PTR_ERR(r_srp)); + SG_LOG(1, fp, "%s: err=%ld\n", __func__, PTR_ERR(r_srp)); if (!IS_ERR(r_srp)) - SG_LOG(4, sfp, "%s: %s r_srp=0x%pK\n", __func__, cp, r_srp); + SG_LOG(4, fp, "%s: %s %sr_srp=0x%pK\n", __func__, cp, + ((r_srp == fp->rsv_srp) ? "[rsv] " : ""), r_srp); return r_srp; } @@ -3341,6 +3342,8 @@ sg_add_sfp(struct sg_device *sdp) __assign_bit(SG_FFD_CMD_Q, sfp->ffd_bm, SG_DEF_COMMAND_Q); __assign_bit(SG_FFD_KEEP_ORPHAN, sfp->ffd_bm, SG_DEF_KEEP_ORPHAN); __assign_bit(SG_FFD_Q_AT_TAIL, sfp->ffd_bm, SG_DEFAULT_Q_AT); + atomic_set(&sfp->submitted, 0); + atomic_set(&sfp->waiting, 0); /* * SG_SCATTER_SZ initializes scatter_elem_sz but different value may * be given as driver/module parameter (e.g. 'scatter_elem_sz=8192').

[v21,30/46] sg: expand sg_comm_wr_t

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