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Subject[PATCH 3/4] Core aio changes to support vectored AIO
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Date
This work is initially done by Zach Brown to add support for
vectored aio. These are the core changes for AIO to support
IOCB_CMD_PREADV/IOCB_CMD_PWRITEV.

I made few extra changes beyond Zach's work. They are
- took out aio_pread/aio_pwrite and made them
a special case into vectored support
- added single inlined vector to save on kmalloc()
for a simple aio_read/aio_write
- kiocb->ki_left always indicates the amount of
IO need to be done. Made sure that this gets
set in sync case also, so that we don't need
to loop over iovecs to figure out IO size all
the time.

Signed-off-by: Badari Pulavarty <pbadari@us.ibm.com>
Signed-off-by: Zach Brown <zach.brown@oracle.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Benjamin LaHaise <bcrl@kvack.org>

fs/aio.c | 165 +++++++++++++++++++++++++++++++++---------------
fs/read_write.c | 127 +++++++++++++++++++++---------------
include/linux/aio.h | 4 +
include/linux/aio_abi.h | 2
include/linux/fs.h | 5 +
5 files changed, 199 insertions(+), 104 deletions(-)
Index: linux-2.6.17-rc3.save/fs/aio.c
===================================================================
--- linux-2.6.17-rc3.save.orig/fs/aio.c 2006-05-10 08:21:48.000000000 -0700
+++ linux-2.6.17-rc3.save/fs/aio.c 2006-05-11 08:22:27.317114536 -0700
@@ -415,6 +415,7 @@ static struct kiocb fastcall *__aio_get_
req->ki_retry = NULL;
req->ki_dtor = NULL;
req->private = NULL;
+ req->ki_iovec = NULL;
INIT_LIST_HEAD(&req->ki_run_list);

/* Check if the completion queue has enough free space to
@@ -460,6 +461,8 @@ static inline void really_put_req(struct

if (req->ki_dtor)
req->ki_dtor(req);
+ if (req->ki_iovec != &req->ki_inline_vec)
+ kfree(req->ki_iovec);
kmem_cache_free(kiocb_cachep, req);
ctx->reqs_active--;

@@ -1301,69 +1304,63 @@ asmlinkage long sys_io_destroy(aio_conte
return -EINVAL;
}

-/*
- * aio_p{read,write} are the default ki_retry methods for
- * IO_CMD_P{READ,WRITE}. They maintains kiocb retry state around potentially
- * multiple calls to f_op->aio_read(). They loop around partial progress
- * instead of returning -EIOCBRETRY because they don't have the means to call
- * kick_iocb().
- */
-static ssize_t aio_pread(struct kiocb *iocb)
+static void aio_advance_iovec(struct kiocb *iocb, ssize_t ret)
{
- struct file *file = iocb->ki_filp;
- struct address_space *mapping = file->f_mapping;
- struct inode *inode = mapping->host;
- ssize_t ret = 0;
+ struct iovec *iov = &iocb->ki_iovec[iocb->ki_cur_seg];

- do {
- iocb->ki_inline_vec.iov_base = iocb->ki_buf;
- iocb->ki_inline_vec.iov_len = iocb->ki_left;
+ BUG_ON(ret <= 0);

- ret = file->f_op->aio_read(iocb, &iocb->ki_inline_vec,
- 1, iocb->ki_pos);
- /*
- * Can't just depend on iocb->ki_left to determine
- * whether we are done. This may have been a short read.
- */
- if (ret > 0) {
- iocb->ki_buf += ret;
- iocb->ki_left -= ret;
+ while (iocb->ki_cur_seg < iocb->ki_nr_segs && ret > 0) {
+ ssize_t this = min(iov->iov_len, ret);
+ iov->iov_base += this;
+ iov->iov_len -= this;
+ iocb->ki_left -= this;
+ ret -= this;
+ if (iov->iov_len == 0) {
+ iocb->ki_cur_seg++;
+ iov++;
}
+ }

- /*
- * For pipes and sockets we return once we have some data; for
- * regular files we retry till we complete the entire read or
- * find that we can't read any more data (e.g short reads).
- */
- } while (ret > 0 && iocb->ki_left > 0 &&
- !S_ISFIFO(inode->i_mode) && !S_ISSOCK(inode->i_mode));
-
- /* This means we must have transferred all that we could */
- /* No need to retry anymore */
- if ((ret == 0) || (iocb->ki_left == 0))
- ret = iocb->ki_nbytes - iocb->ki_left;
-
- return ret;
+ /* the caller should not have done more io than what fit in
+ * the remaining iovecs */
+ BUG_ON(ret > 0 && iocb->ki_left == 0);
}

-/* see aio_pread() */
-static ssize_t aio_pwrite(struct kiocb *iocb)
+static ssize_t aio_rw_vect_retry(struct kiocb *iocb)
{
struct file *file = iocb->ki_filp;
+ struct address_space *mapping = file->f_mapping;
+ struct inode *inode = mapping->host;
+ ssize_t (*rw_op)(struct kiocb *, const struct iovec *,
+ unsigned long, loff_t);
ssize_t ret = 0;
+ unsigned short opcode;
+
+ if ((iocb->ki_opcode == IOCB_CMD_PREADV) ||
+ (iocb->ki_opcode == IOCB_CMD_PREAD)) {
+ rw_op = file->f_op->aio_read;
+ opcode = IOCB_CMD_PREADV;
+ } else {
+ rw_op = file->f_op->aio_write;
+ opcode = IOCB_CMD_PWRITEV;
+ }

do {
- iocb->ki_inline_vec.iov_base = iocb->ki_buf;
- iocb->ki_inline_vec.iov_len = iocb->ki_left;
+ ret = rw_op(iocb, &iocb->ki_iovec[iocb->ki_cur_seg],
+ iocb->ki_nr_segs - iocb->ki_cur_seg,
+ iocb->ki_pos);
+ if (ret > 0)
+ aio_advance_iovec(iocb, ret);

- ret = file->f_op->aio_write(iocb, &iocb->ki_inline_vec,
- 1, iocb->ki_pos);
- if (ret > 0) {
- iocb->ki_buf += ret;
- iocb->ki_left -= ret;
- }
- } while (ret > 0 && iocb->ki_left > 0);
+ /* retry all partial writes. retry partial reads as long as its a
+ * regular file. */
+ } while (ret > 0 && iocb->ki_left > 0 &&
+ (opcode == IOCB_CMD_PWRITEV ||
+ (!S_ISFIFO(inode->i_mode) && !S_ISSOCK(inode->i_mode))));

+ /* This means we must have transferred all that we could */
+ /* No need to retry anymore */
if ((ret == 0) || (iocb->ki_left == 0))
ret = iocb->ki_nbytes - iocb->ki_left;

@@ -1390,6 +1387,38 @@ static ssize_t aio_fsync(struct kiocb *i
return ret;
}

+static ssize_t aio_setup_vectored_rw(struct kiocb *kiocb)
+{
+ ssize_t ret;
+
+ ret = rw_copy_check_uvector((struct iovec __user *)kiocb->ki_buf,
+ kiocb->ki_nbytes, 1,
+ &kiocb->ki_inline_vec, &kiocb->ki_iovec);
+ if (ret < 0)
+ goto out;
+
+ kiocb->ki_nr_segs = kiocb->ki_nbytes;
+ kiocb->ki_cur_seg = 0;
+ /* ki_nbytes/left now reflect bytes instead of segs */
+ kiocb->ki_nbytes = ret;
+ kiocb->ki_left = ret;
+
+ ret = 0;
+out:
+ return ret;
+}
+
+static ssize_t aio_setup_single_vector(struct kiocb *kiocb)
+{
+ kiocb->ki_iovec = &kiocb->ki_inline_vec;
+ kiocb->ki_iovec->iov_base = kiocb->ki_buf;
+ kiocb->ki_iovec->iov_len = kiocb->ki_left;
+ kiocb->ki_nr_segs = 1;
+ kiocb->ki_cur_seg = 0;
+ kiocb->ki_nbytes = kiocb->ki_left;
+ return 0;
+}
+
/*
* aio_setup_iocb:
* Performs the initial checks and aio retry method
@@ -1412,9 +1441,12 @@ static ssize_t aio_setup_iocb(struct kio
ret = security_file_permission(file, MAY_READ);
if (unlikely(ret))
break;
+ ret = aio_setup_single_vector(kiocb);
+ if (ret)
+ break;
ret = -EINVAL;
if (file->f_op->aio_read)
- kiocb->ki_retry = aio_pread;
+ kiocb->ki_retry = aio_rw_vect_retry;
break;
case IOCB_CMD_PWRITE:
ret = -EBADF;
@@ -1427,9 +1459,40 @@ static ssize_t aio_setup_iocb(struct kio
ret = security_file_permission(file, MAY_WRITE);
if (unlikely(ret))
break;
+ ret = aio_setup_single_vector(kiocb);
+ if (ret)
+ break;
+ ret = -EINVAL;
+ if (file->f_op->aio_write)
+ kiocb->ki_retry = aio_rw_vect_retry;
+ break;
+ case IOCB_CMD_PREADV:
+ ret = -EBADF;
+ if (unlikely(!(file->f_mode & FMODE_READ)))
+ break;
+ ret = security_file_permission(file, MAY_READ);
+ if (unlikely(ret))
+ break;
+ ret = aio_setup_vectored_rw(kiocb);
+ if (ret)
+ break;
+ ret = -EINVAL;
+ if (file->f_op->aio_read)
+ kiocb->ki_retry = aio_rw_vect_retry;
+ break;
+ case IOCB_CMD_PWRITEV:
+ ret = -EBADF;
+ if (unlikely(!(file->f_mode & FMODE_WRITE)))
+ break;
+ ret = security_file_permission(file, MAY_WRITE);
+ if (unlikely(ret))
+ break;
+ ret = aio_setup_vectored_rw(kiocb);
+ if (ret)
+ break;
ret = -EINVAL;
if (file->f_op->aio_write)
- kiocb->ki_retry = aio_pwrite;
+ kiocb->ki_retry = aio_rw_vect_retry;
break;
case IOCB_CMD_FDSYNC:
ret = -EINVAL;
Index: linux-2.6.17-rc3.save/include/linux/aio.h
===================================================================
--- linux-2.6.17-rc3.save.orig/include/linux/aio.h 2006-05-10 08:21:48.000000000 -0700
+++ linux-2.6.17-rc3.save/include/linux/aio.h 2006-05-10 08:29:26.000000000 -0700
@@ -7,6 +7,7 @@
#include <linux/uio.h>

#include <asm/atomic.h>
+#include <linux/uio.h>

#define AIO_MAXSEGS 4
#define AIO_KIOGRP_NR_ATOMIC 8
@@ -114,6 +115,9 @@ struct kiocb {
long ki_kicked; /* just for testing */
long ki_queued; /* just for testing */
struct iovec ki_inline_vec; /* inline vector */
+ struct iovec *ki_iovec;
+ unsigned long ki_nr_segs;
+ unsigned long ki_cur_seg;

struct list_head ki_list; /* the aio core uses this
* for cancellation */
Index: linux-2.6.17-rc3.save/include/linux/aio_abi.h
===================================================================
--- linux-2.6.17-rc3.save.orig/include/linux/aio_abi.h 2006-05-10 08:21:48.000000000 -0700
+++ linux-2.6.17-rc3.save/include/linux/aio_abi.h 2006-05-10 08:29:26.000000000 -0700
@@ -41,6 +41,8 @@ enum {
* IOCB_CMD_POLL = 5,
*/
IOCB_CMD_NOOP = 6,
+ IOCB_CMD_PREADV = 7,
+ IOCB_CMD_PWRITEV = 8,
};

/* read() from /dev/aio returns these structures. */
Index: linux-2.6.17-rc3.save/fs/read_write.c
===================================================================
--- linux-2.6.17-rc3.save.orig/fs/read_write.c 2006-05-10 08:23:47.000000000 -0700
+++ linux-2.6.17-rc3.save/fs/read_write.c 2006-05-11 08:22:04.191630144 -0700
@@ -508,6 +508,74 @@ ssize_t do_loop_readv_writev(struct file
return ret;
}

+ssize_t rw_copy_check_uvector(const struct iovec __user * uvector,
+ unsigned long nr_segs, unsigned long fast_segs,
+ struct iovec *fast_pointer,
+ struct iovec **ret_pointer)
+ {
+ unsigned long seg;
+ ssize_t ret;
+ struct iovec *iov = fast_pointer;
+
+ /*
+ * SuS says "The readv() function *may* fail if the iovcnt argument
+ * was less than or equal to 0, or greater than {IOV_MAX}. Linux has
+ * traditionally returned zero for zero segments, so...
+ */
+ if (nr_segs == 0) {
+ ret = 0;
+ goto out;
+ }
+
+ /*
+ * First get the "struct iovec" from user memory and
+ * verify all the pointers
+ */
+ if ((nr_segs > UIO_MAXIOV) || (nr_segs <= 0)) {
+ ret = -EINVAL;
+ goto out;
+ }
+ if (nr_segs > fast_segs) {
+ iov = kmalloc(nr_segs*sizeof(struct iovec), GFP_KERNEL);
+ if (iov == NULL) {
+ ret = -ENOMEM;
+ goto out;
+ }
+ }
+ if (copy_from_user(iov, uvector, nr_segs*sizeof(*uvector))) {
+ ret = -EFAULT;
+ goto out;
+ }
+
+ /*
+ * According to the Single Unix Specification we should return EINVAL
+ * if an element length is < 0 when cast to ssize_t or if the
+ * total length would overflow the ssize_t return value of the
+ * system call.
+ */
+ ret = 0;
+ for (seg = 0; seg < nr_segs; seg++) {
+ void __user *buf = iov[seg].iov_base;
+ ssize_t len = (ssize_t)iov[seg].iov_len;
+
+ /* see if we we're about to use an invalid len or if
+ * it's about to overflow ssize_t */
+ if (len < 0 || (ret + len < ret)) {
+ ret = -EINVAL;
+ goto out;
+ }
+ if (unlikely(!access_ok(vrfy_dir(type), buf, len))) {
+ ret = -EFAULT;
+ goto out;
+ }
+
+ ret += len;
+ }
+out:
+ *ret_pointer = iov;
+ return ret;
+}
+
/* A write operation does a read from user space and vice versa */
#define vrfy_dir(type) ((type) == READ ? VERIFY_WRITE : VERIFY_READ)

@@ -519,64 +587,20 @@ static ssize_t do_readv_writev(int type,
struct iovec iovstack[UIO_FASTIOV];
struct iovec *iov = iovstack;
ssize_t ret;
- int seg;
io_fn_t fn;
iov_fn_t fnv;

- /*
- * SuS says "The readv() function *may* fail if the iovcnt argument
- * was less than or equal to 0, or greater than {IOV_MAX}. Linux has
- * traditionally returned zero for zero segments, so...
- */
- ret = 0;
- if (nr_segs == 0)
+ if (!file->f_op) {
+ ret = -EINVAL;
goto out;
-
- /*
- * First get the "struct iovec" from user memory and
- * verify all the pointers
- */
- ret = -EINVAL;
- if (nr_segs > UIO_MAXIOV)
- goto out;
- if (!file->f_op)
- goto out;
- if (nr_segs > UIO_FASTIOV) {
- ret = -ENOMEM;
- iov = kmalloc(nr_segs*sizeof(struct iovec), GFP_KERNEL);
- if (!iov)
- goto out;
}
- ret = -EFAULT;
- if (copy_from_user(iov, uvector, nr_segs*sizeof(*uvector)))
- goto out;

- /*
- * Single unix specification:
- * We should -EINVAL if an element length is not >= 0 and fitting an
- * ssize_t. The total length is fitting an ssize_t
- *
- * Be careful here because iov_len is a size_t not an ssize_t
- */
- tot_len = 0;
- ret = -EINVAL;
- for (seg = 0; seg < nr_segs; seg++) {
- void __user *buf = iov[seg].iov_base;
- ssize_t len = (ssize_t)iov[seg].iov_len;
-
- if (len < 0) /* size_t not fitting an ssize_t .. */
- goto out;
- if (unlikely(!access_ok(vrfy_dir(type), buf, len)))
- goto Efault;
- tot_len += len;
- if ((ssize_t)tot_len < 0) /* maths overflow on the ssize_t */
- goto out;
- }
- if (tot_len == 0) {
- ret = 0;
+ ret = rw_copy_check_uvector(uvector, nr_segs, ARRAY_SIZE(iovstack),
+ iovstack, &iov);
+ if (ret <= 0)
goto out;
- }

+ tot_len = ret;
ret = rw_verify_area(type, file, pos, tot_len);
if (ret < 0)
goto out;
@@ -608,9 +632,6 @@ out:
fsnotify_modify(file->f_dentry);
}
return ret;
-Efault:
- ret = -EFAULT;
- goto out;
}

ssize_t vfs_readv(struct file *file, const struct iovec __user *vec,
Index: linux-2.6.17-rc3.save/include/linux/fs.h
===================================================================
--- linux-2.6.17-rc3.save.orig/include/linux/fs.h 2006-05-10 08:23:47.000000000 -0700
+++ linux-2.6.17-rc3.save/include/linux/fs.h 2006-05-11 08:22:04.192629992 -0700
@@ -1068,6 +1068,11 @@ struct inode_operations {

struct seq_file;

+ssize_t rw_copy_check_uvector(const struct iovec __user * uvector,
+ unsigned long nr_segs, unsigned long fast_segs,
+ struct iovec *fast_pointer,
+ struct iovec **ret_pointer);
+
extern ssize_t vfs_read(struct file *, char __user *, size_t, loff_t *);
extern ssize_t vfs_write(struct file *, const char __user *, size_t, loff_t *);
extern ssize_t vfs_readv(struct file *, const struct iovec __user *,

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