从ATA层向设备发送TRIM命令
ATA TRIM命令是文件系统用来通知设备哪些逻辑地址不再被占用，可以被设备回收为空闲空间，在ATA命令集中，TRIM命令只是DATAMANAGEMENT SET（DMS）命令的一个子命令，DMS命令是专门用来做设备优化的（The DATA SET MANAGEMENT command provides information for deviceoptimization (e.g., file system information)，如图1所示，当DMS的feature属性最低位置1，发送的就是TRIM命令。
TRIM命令的传送过程中，通过入口的方式传递需要告诉设备的LBA地址，比如需要告诉设备第11至18个block可以回收，在DMA的写buffer中共需8个字节，高16bit为len值8， 低48位为LBA起始地址11。 每个入口的长度因为用2个字节16bits表示，然后全0的reserved，所以每个入口最多可以表示65535个blocks，如需单次通知设备更多地址，就会再相应增加一个入口。
图1. DMS命令ATA格式
发送ata_trim命令的代码如下，需要把它放到一个和内核一起编译的模块中，通过/proc/变量的值输入进行调用。 感兴趣的话，可以一起讨论喔
int ata_trim(uint block, uint n_block){struct ata_queued_cmd *qc=NULL;struct ata_taskfile *tf =NULL; struct sg_table *table=kmalloc(sizeof(struct sg_table),GFP_ATOMIC);int rc=0, nents=1; //entry(sg list) number of scatter/gathering list in sg_tablestruct page *pg_pt;u32 size;void *buf;//transfer buffer to send lba addresses...if(ata_dev_lookup())goto error_exit;/*allocate an ata cmd structure from the ata port*/qc = ata_qc_new_init(dev);if(unlikely(!qc))goto error_exit;/*allocate sg_table and sg list*/allocate_mempool();rc = __sg_alloc_table(table, nents, SCSI_MAX_SG_SEGMENTS,GFP_ATOMIC, scsi_sg_alloc);if (unlikely(rc)){__sg_free_table(table, SCSI_MAX_SG_SEGMENTS,scsi_sg_free);goto error_exit;}pg_pt=alloc_pages(GFP_ATOMIC,0); //allocate 1page: 4k dataspace...if(!pg_pt)goto error_exit;printk("\nStarting block is : %lu , blocks count is : %d \n\n", block, n_block);sg_set_page(table->sgl, pg_pt, 8, 0);// 8 bytes for 1 trim entrytable->nents=1;table->orig_nents=1;ata_sg_init(qc,table->sgl,1); qc->scsidone=my_scsidone; qc->complete_fn=my_ata_scsi_qc_complete;//orignally for write_same of multiple areas... now to transfer only one LBA...buf = page_address(sg_page(table->sgl));if(!buf)goto error_exit;//size is the used bytes and it is the size for DMA to transfersize = ata_set_lba_range_entries(buf, 4096, block, n_block);qc->dma_dir=DMA_TO_DEVICE;qc->nbytes=size;//data size in bytes to be transferedtf=&qc->tf;tf->protocol = ATA_PROT_DMA;tf->hob_feature = 0;tf->feature = ATA_DSM_TRIM;tf->hob_nsect = (size / 512) >> 8;tf->nsect = size / 512;tf->command = ATA_CMD_DSM;tf->flags |= ATA_TFLAG_ISADDR | ATA_TFLAG_DEVICE | ATA_TFLAG_LBA48 | ATA_TFLAG_WRITE;if(!qc->sg || !qc->n_elem || !qc->nbytes)goto error_exit;ata_qc_issue(qc);mdelay(800);qc_error_disp(qc->err_mask);return 0;error_exit:printk("\n\nTO client--------------Getting Resourcesfailed----------------- \n\n");return 1;}