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    SubjectRe: [PATCH 3/3] tcm/fileio: Add UNMAP / Block DISCARD support
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    On Tue, 2010-09-28 at 08:46 +0200, Boaz Harrosh wrote:
    > On 09/28/2010 12:51 AM, Nicholas A. Bellinger wrote:
    > > From: Nicholas Bellinger <nab@linux-iscsi.org>
    > >
    > > This patch adds UNMAP emulation support using Block layer DISCARD in fd_emulate_scsi_cdb()
    > > -> transport_generic_unmap(). This includes the use of blk_queue_discard() in
    > > fd_create_virtdevice() to determine when to set DEV_ATTRIB(dev)->emulate_tpe=1 to
    > > signal to TCM Core to perform the necessary control CDB emulation for TPE=1 / UNMAP.
    > >
    > > Note this patch igrab() + iput() when accessing struct block_device via
    > > I_BDEV(file->f_mapping->host) that is required for transport_generic_unmap()
    > > within fd_emulate_scsi_cdb().
    > >
    > > Also note that when (S_ISBLK(inode->i_mode) is NULL, the TPE=1 and UNMAP emulation
    > > are disabled for non BD struct file I/O.
    > >
    > > Signed-off-by: Nicholas A. Bellinger <nab@linux-iscsi.org>
    > > ---
    > > drivers/target/target_core_file.c | 53 ++++++++++++++++++++++++++++++++++++-
    > > 1 files changed, 52 insertions(+), 1 deletions(-)
    > >
    > > diff --git a/drivers/target/target_core_file.c b/drivers/target/target_core_file.c
    > > index 93d3f63..3b91556 100644
    > > --- a/drivers/target/target_core_file.c
    > > +++ b/drivers/target/target_core_file.c
    > > @@ -235,6 +235,17 @@ static struct se_device *fd_create_virtdevice(
    > >
    > > fd_dev->fd_dev_id = fd_host->fd_host_dev_id_count++;
    > > fd_dev->fd_queue_depth = dev->queue_depth;
    > > + /*
    > > + * Check for QUEUE_FLAG_DISCARD and enable TCM TPE emulation
    > > + * if present for struct block_device backend
    > > + */
    > > + if (S_ISBLK(inode->i_mode)) {
    > > + if (blk_queue_discard(bdev_get_queue(inode->i_bdev))) {
    > > + DEV_ATTRIB(dev)->emulate_tpe = 1;
    > > + printk(KERN_INFO "FILEIO: Enabling BLOCK Discard"
    > > + " and TPE=1 emulation\n");
    > > + }
    > > + }
    > >
    > > printk(KERN_INFO "CORE_FILE[%u] - Added TCM FILEIO Device ID: %u at %s,"
    > > " %llu total bytes\n", fd_host->fd_host_id, fd_dev->fd_dev_id,
    > > @@ -388,9 +399,13 @@ static int fd_emulate_read_cap16(struct se_task *task)
    > > */
    > > static int fd_emulate_scsi_cdb(struct se_task *task)
    > > {
    > > - int ret;
    > > struct se_cmd *cmd = TASK_CMD(task);
    > > + struct fd_dev *fd_dev = (struct fd_dev *) task->se_dev->dev_ptr;
    >
    > No need to typecast a void pointer

    Whoops, this was a cut and paste but these unnecessary typecasts for
    'struct sub_dev' and 'struct sub_task' have been around forever and can
    go. Removing these in target_core_file.c, target_core_iblock,
    target_core_pscsi.c target_core_rd.c, and target_core_stgt.c now.

    >
    > > struct fd_request *fd_req = (struct fd_request *) task->transport_req;
    > > + struct file *f = fd_dev->fd_file;
    > > + struct inode *i;
    > > + struct block_device *bd;
    > > + int ret;
    > >
    > > switch (fd_req->fd_scsi_cdb[0]) {
    > > case INQUIRY:
    > > @@ -433,6 +448,42 @@ static int fd_emulate_scsi_cdb(struct se_task *task)
    > > if (ret < 0)
    > > return ret;
    > > break;
    > > + case UNMAP:
    > > + i = igrab(f->f_mapping->host);
    > > + if (!(i)) {
    >
    > You must have a reference on your fileio backend file, right?
    > This could be a BUG_ON()

    Yes, this was an extra bit of paranoia as we always expect to have a
    valid struct file here.

    >
    > > + printk(KERN_ERR "FILEIO: Unable to locate inode for"
    > > + " backend for UNMAP\n");
    > > + return PYX_TRANSPORT_LU_COMM_FAILURE;
    > > + }
    > > + /*
    > > + * Currently for struct file w/o a struct block_device
    > > + * backend we return a success..
    > > + */
    > > + if (!(S_ISBLK(i->i_mode))) {
    >
    > I did not see in the first patch that you do this check when actually sending
    > the VPD page. I only saw that it is enabled if set from configfs. (Sorry for
    > the noise if I missed it). So you might want to call a target specific function
    > when sending the VPD page. This way this will never happen right?

    That is correct, once we determine that fd_create_virtdevice() ->
    blk_queue_discard() is going to set DEV_ATTRIB(dev)->emulate_tpe=1, this
    is what will signal TPE=1 in SA READ_CAPACITY_16 and other locations in
    Patch 1 for the emulated case with TCM/IBLOCK and TCM/FILEIO.

    >
    > > + printk(KERN_WARNING "Ignoring UNMAP for non BD"
    > > + " backend for struct file\n");
    >
    > TODO: Lots of extent based filesystems could enjoy if you punch an hole
    > in the file. (Which will also send a proper discard).
    > So how to punch an hole in a file via vfs?

    Good question, as all of the current block discard support assumes a
    struct block_device * pointer currently.

    I know that hch has mentioned that accesing a struct block_device from
    struct file is very dangerous, but I am assuming for the TCM/FILEIO case
    that this code will be protected by igrab() and iput().

    hch and jaxboe, any comments here..?

    Thanks!

    --nab

    >
    > > + iput(i);
    > > + return PYX_TRANSPORT_LU_COMM_FAILURE;
    > > + }
    > > + bd = I_BDEV(f->f_mapping->host);
    > > + if (!(bd)) {
    > > + printk(KERN_ERR "FILEIO: Unable to locate struct"
    > > + " block_device for UNMAP\n");
    > > + iput(i);
    > > + return PYX_TRANSPORT_LU_COMM_FAILURE;
    > > + }
    > > + /*
    > > + * Now call the transport_generic_unmap() -> blkdev_issue_discard()
    > > + * wrapper to translate SCSI UNMAP into Linux/BLOCK discards on
    > > + * LBA+Range descriptors in the UNMAP write paylaod.
    > > + */
    > > + ret = transport_generic_unmap(cmd, bd);
    > > + if (ret < 0) {
    > > + iput(i);
    > > + return ret;
    > > + }
    > > + iput(i);
    > > + break;
    > > case ALLOW_MEDIUM_REMOVAL:
    > > case ERASE:
    > > case REZERO_UNIT:
    >
    > Boaz
    >



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