Re: [PATCH v6 1/4] libata: Safely overwrite attached page in WRITE SAME xlat

Tom Yan
2016-08-22T20:14:02Z

Oh, 0xffff is fine for me, as long as you change it in
ata_scsiop_inq_b0 as well. Actually I think replacing it with a macro
(as suggested by Martin in another thread) is a good idea as well. A
line split would be better than introducing an unnecessary variable
that costs readability in the logic sense.

On 23 August 2016 at 03:51, Shaun Tancheff <shaun.tancheff@seagate.com> wrote:
> On Mon, Aug 22, 2016 at 2:27 PM, Tom Yan <tom.ty89@gmail.com> wrote:
>> On 22 August 2016 at 12:23, Shaun Tancheff <shaun@tancheff.com> wrote:
>>> Safely overwriting the attached page to ATA format from the SCSI formatted
>>> variant.
>>>
>>> Signed-off-by: Shaun Tancheff <shaun.tancheff@seagate.com>
>>> ---
>>> v6:
>>> - Fix bisect bug reported by Tom Yan <tom.ty89@gmail.com>
>>> - Change to use sg_copy_from_buffer as per Christoph Hellwig <hch@lst.de>
>>> v5:
>>> - Added prep patch to work with non-page aligned scatterlist pages
>>> and use kmap_atomic() to lock page during modification.
>>>
>>> drivers/ata/libata-scsi.c | 56 ++++++++++++++++++++++++++++++++++++++++++-----
>>> include/linux/ata.h | 26 ----------------------
>>> 2 files changed, 51 insertions(+), 31 deletions(-)
>>>
>>> diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
>>> index e207b33..7990cb2 100644
>>> --- a/drivers/ata/libata-scsi.c
>>> +++ b/drivers/ata/libata-scsi.c
>>> @@ -3282,6 +3282,54 @@ static unsigned int ata_scsi_pass_thru(struct ata_queued_cmd *qc)
>>> return 1;
>>> }
>>>
>>> +/**
>>> + * ata_format_dsm_trim_descr() - SATL Write Same to DSM Trim
>>> + * @cmd: SCSI command being translated
>>> + * @num: Maximum number of entries (nominally 64).
>>> + * @sector: Starting sector
>>> + * @count: Total Range of request
>>> + *
>>> + * Rewrite the WRITE SAME descriptor to be a DSM TRIM little-endian formatted
>>> + * descriptor.
>>> + *
>>> + * Upto 64 entries of the format:
>>> + * 63:48 Range Length
>>> + * 47:0 LBA
>>> + *
>>> + * Range Length of 0 is ignored.
>>> + * LBA's should be sorted order and not overlap.
>>> + *
>>> + * NOTE: this is the same format as ADD LBA(S) TO NV CACHE PINNED SET
>>> + */
>>> +static unsigned int ata_format_dsm_trim_descr(struct scsi_cmnd *cmd, u32 num,
>>> + u64 sector, u32 count)
>>> +{
>>> + __le64 *buffer;
>>> + u32 i = 0, used_bytes;
>>> + unsigned long flags;
>>> +
>>> + BUILD_BUG_ON(512 > ATA_SCSI_RBUF_SIZE);
>>> +
>>> + spin_lock_irqsave(&ata_scsi_rbuf_lock, flags);
>>> + buffer = ((void *)ata_scsi_rbuf);
>>> + while (i < num) {
>>> + u64 entry = sector |
>>> + ((u64)(count > 0xffff ? 0xffff : count) << 48);
>>> + buffer[i++] = __cpu_to_le64(entry);
>>> + if (count <= 0xffff)
>>> + break;
>>> + count -= 0xffff;
>>> + sector += 0xffff;
>>> + }
>>> +
>>> + used_bytes = ALIGN(i * 8, 512);
>>> + memset(buffer + i, 0, used_bytes - i * 8);
>>> + sg_copy_from_buffer(scsi_sglist(cmd), scsi_sg_count(cmd), buffer, 512);
>>> + spin_unlock_irqrestore(&ata_scsi_rbuf_lock, flags);
>>> +
>>> + return used_bytes;
>>> +}
>>> +
>>> static unsigned int ata_scsi_write_same_xlat(struct ata_queued_cmd *qc)
>>> {
>>> struct ata_taskfile *tf = &qc->tf;
>>> @@ -3290,8 +3338,8 @@ static unsigned int ata_scsi_write_same_xlat(struct ata_queued_cmd *qc)
>>> const u8 *cdb = scmd->cmnd;
>>> u64 block;
>>> u32 n_block;
>>> + const u32 trmax = ATA_MAX_TRIM_RNUM;
>>
>> This does not seem like a good idea.
>>
>>> u32 size;
>>> - void *buf;
>>> u16 fp;
>>> u8 bp = 0xff;
>>>
>>> @@ -3319,10 +3367,8 @@ static unsigned int ata_scsi_write_same_xlat(struct ata_queued_cmd *qc)
>>> if (!scsi_sg_count(scmd))
>>> goto invalid_param_len;
>>>
>>> - buf = page_address(sg_page(scsi_sglist(scmd)));
>>> -
>>> - if (n_block <= 65535 * ATA_MAX_TRIM_RNUM) {
>>> - size = ata_set_lba_range_entries(buf, ATA_MAX_TRIM_RNUM, block, n_block);
>>> + if (n_block <= 0xffff * trmax) {
>>
>> Note that the limit here would always be the advertised Maximum Write
>> Same Length (ata_scsiop_inq_b0). It would be best for them to look the
>> same. Besides, it doesn't seem necessary to create this trmax anyway.
>
> It is entirely a style thing. I tend to prefer hex when describing an interface
> that specifies number of bits. The trmax is just to keep the following line
> under 80 chars.
> I am not tied to either. I can change it if people really find it confusing.
>
>>> + size = ata_format_dsm_trim_descr(scmd, trmax, block, n_block);
>>> } else {
>>> fp = 2;
>>> goto invalid_fld;
>>> diff --git a/include/linux/ata.h b/include/linux/ata.h
>>> index adbc812..45a1d71 100644
>>> --- a/include/linux/ata.h
>>> +++ b/include/linux/ata.h
>>> @@ -1071,32 +1071,6 @@ static inline void ata_id_to_hd_driveid(u16 *id)
>>> #endif
>>> }
>>>
>>> -/*
>>> - * Write LBA Range Entries to the buffer that will cover the extent from
>>> - * sector to sector + count. This is used for TRIM and for ADD LBA(S)
>>> - * TO NV CACHE PINNED SET.
>>> - */
>>> -static inline unsigned ata_set_lba_range_entries(void *_buffer,
>>> - unsigned num, u64 sector, unsigned long count)
>>> -{
>>> - __le64 *buffer = _buffer;
>>> - unsigned i = 0, used_bytes;
>>> -
>>> - while (i < num) {
>>> - u64 entry = sector |
>>> - ((u64)(count > 0xffff ? 0xffff : count) << 48);
>>> - buffer[i++] = __cpu_to_le64(entry);
>>> - if (count <= 0xffff)
>>> - break;
>>> - count -= 0xffff;
>>> - sector += 0xffff;
>>> - }
>>> -
>>> - used_bytes = ALIGN(i * 8, 512);
>>> - memset(buffer + i, 0, used_bytes - i * 8);
>>> - return used_bytes;
>>> -}
>>> -
>>> static inline bool ata_ok(u8 status)
>>> {
>>> return ((status & (ATA_BUSY | ATA_DRDY | ATA_DF | ATA_DRQ | ATA_ERR))
>>> --
>>> 2.9.3
>>>
>
>
>
> --
> Shaun Tancheff