[PATCH 1/2 V2] kvm tools: Add scatter-gather variants of IO functions

[Sasha Levin <levinsasha928@gmail.com>]

Added scatter-gather variants of [x,xp][read,write]() and [p]read_in_full().

Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
---
 tools/kvm/include/kvm/read-write.h |   13 +++
 tools/kvm/read-write.c             |  172 ++++++++++++++++++++++++++++++++++++
 2 files changed, 185 insertions(+), 0 deletions(-)

diff --git a/tools/kvm/include/kvm/read-write.h b/tools/kvm/include/kvm/read-write.h
index 069326b..3351103 100644
--- a/tools/kvm/include/kvm/read-write.h
+++ b/tools/kvm/include/kvm/read-write.h
@@ -2,6 +2,7 @@
 #define KVM_READ_WRITE_H
 
 #include <sys/types.h>
+#include <sys/uio.h>
 #include <unistd.h>
 
 ssize_t xread(int fd, void *buf, size_t count);
@@ -16,4 +17,16 @@ ssize_t xpwrite(int fd, const void *buf, size_t count, off_t offset);
 ssize_t pread_in_full(int fd, void *buf, size_t count, off_t offset);
 ssize_t pwrite_in_full(int fd, const void *buf, size_t count, off_t offset);
 
+ssize_t xreadv(int fd, const struct iovec *iov, int iovcnt);
+ssize_t xwritev(int fd, const struct iovec *iov, int iovcnt);
+
+ssize_t readv_in_full(int fd, const struct iovec *iov, int iovcnt);
+ssize_t writev_in_full(int fd, const struct iovec *iov, int iovcnt);
+
+ssize_t xpreadv(int fd, const struct iovec *iov, int iovcnt, off_t offset);
+ssize_t xpwritev(int fd, const struct iovec *iov, int iovcnt, off_t offset);
+
+ssize_t preadv_in_full(int fd, const struct iovec *iov, int iovcnt, off_t offset);
+ssize_t pwritev_in_full(int fd, const struct iovec *iov, int iovcnt, off_t offset);
+
 #endif /* KVM_READ_WRITE_H */
diff --git a/tools/kvm/read-write.c b/tools/kvm/read-write.c
index 398918b..449e8a2 100644
--- a/tools/kvm/read-write.c
+++ b/tools/kvm/read-write.c
@@ -152,3 +152,175 @@ ssize_t pwrite_in_full(int fd, const void *buf, size_t count, off_t offset)
 
 	return total;
 }
+
+/* Same as readv(2) except that this function never returns EAGAIN or EINTR. */
+ssize_t xreadv(int fd, const struct iovec *iov, int iovcnt)
+{
+	ssize_t nr;
+
+restart:
+	nr = readv(fd, iov, iovcnt);
+	if ((nr < 0) && ((errno == EAGAIN) || (errno == EINTR)))
+		goto restart;
+
+	return nr;
+}
+
+/* Same as writev(2) except that this function never returns EAGAIN or EINTR. */
+ssize_t xwritev(int fd, const struct iovec *iov, int iovcnt)
+{
+	ssize_t nr;
+
+restart:
+	nr = write(fd, iov, iovcnt);
+	if ((nr < 0) && ((errno == EAGAIN) || (errno == EINTR)))
+		goto restart;
+
+	return nr;
+}
+
+static inline ssize_t get_iov_size(const struct iovec *iov, int iovcnt)
+{
+	size_t size = 0;
+	while (iovcnt--)
+		size += (iov++)->iov_len;
+
+	return size;
+}
+
+ssize_t readv_in_full(int fd, const struct iovec *iov, int iovcnt)
+{
+	ssize_t total = 0;
+	ssize_t count = get_iov_size(iov, iovcnt);
+
+	while (count > 0) {
+		ssize_t nr;
+
+		nr = xreadv(fd, iov, iovcnt);
+		if (nr <= 0) {
+			if (total > 0)
+				return total;
+
+			return -1;
+		}
+
+		while ((size_t)nr >= iov->iov_len) {
+			nr -= iov->iov_len;
+			total += iov->iov_len;
+			count -= iov->iov_len;
+			iovcnt--;
+			iov++;
+		}
+	}
+
+	return total;
+}
+
+ssize_t writev_in_full(int fd, const struct iovec *iov, int iovcnt)
+{
+	ssize_t total = 0;
+	size_t count = get_iov_size(iov, iovcnt);
+
+	while (count > 0) {
+		ssize_t nr;
+
+		nr = xwritev(fd, iov, iovcnt);
+		if (nr < 0)
+			return -1;
+		if (nr == 0) {
+			errno = ENOSPC;
+			return -1;
+		}
+
+		while ((size_t)nr >= iov->iov_len) {
+			nr -= iov->iov_len;
+			total += iov->iov_len;
+			count -= iov->iov_len;
+			iovcnt--;
+			iov++;
+		}
+	}
+
+	return total;
+}
+
+/* Same as preadv(2) except that this function never returns EAGAIN or EINTR. */
+ssize_t xpreadv(int fd, const struct iovec *iov, int iovcnt, off_t offset)
+{
+	ssize_t nr;
+
+restart:
+	nr = preadv(fd, iov, iovcnt, offset);
+	if ((nr < 0) && ((errno == EAGAIN) || (errno == EINTR)))
+		goto restart;
+
+	return nr;
+}
+
+/* Same as pwritev(2) except that this function never returns EAGAIN or EINTR. */
+ssize_t xpwritev(int fd, const struct iovec *iov, int iovcnt, off_t offset)
+{
+	ssize_t nr;
+
+restart:
+	nr = pwritev(fd, iov, iovcnt, offset);
+	if ((nr < 0) && ((errno == EAGAIN) || (errno == EINTR)))
+		goto restart;
+
+	return nr;
+}
+
+ssize_t preadv_in_full(int fd, const struct iovec *iov, int iovcnt, off_t offset)
+{
+	ssize_t total = 0;
+	size_t count = get_iov_size(iov, iovcnt);
+
+	while (count > 0) {
+		ssize_t nr;
+
+		nr = xpreadv(fd, iov, iovcnt, offset);
+		if (nr <= 0) {
+			if (total > 0)
+				return total;
+
+			return -1;
+		}
+
+		while ((size_t)nr >= iov->iov_len) {
+			nr -= iov->iov_len;
+			total += iov->iov_len;
+			count -= iov->iov_len;
+			iovcnt--;
+			iov++;
+		}
+	}
+
+	return total;
+}
+
+ssize_t pwritev_in_full(int fd, const struct iovec *iov, int iovcnt, off_t offset)
+{
+	ssize_t total = 0;
+	size_t count = get_iov_size(iov, iovcnt);
+
+	while (count > 0) {
+		ssize_t nr;
+
+		nr = xpwritev(fd, iov, iovcnt, offset);
+		if (nr < 0)
+			return -1;
+		if (nr == 0) {
+			errno = ENOSPC;
+			return -1;
+		}
+		while ((size_t)nr >= iov->iov_len) {
+			nr -= iov->iov_len;
+			total += iov->iov_len;
+			count -= iov->iov_len;
+			iovcnt--;
+			iov++;
+		}
+	}
+
+	return total;
+}
-- 
1.7.5.rc1