[Tarantool-patches] [PATCH v2] fio/coio: handle partial writes

[Cyrill Gorcunov <gorcunov@gmail.com>]

Writing less bytes than requested is perfectly fine. In turn out
that fio.write/pwrite api simply returns 'true' even if only some
part of a buffer has been written.

Thus make coio_write and coio_pwrite to write the whole data in
a cycle. Note in most situations there will be only one pass,
partial writes are really the rare cases.

Note that we're not handling nonblocking writes here (which
could return EAGAIN) simply because we need an other api
which would accept timeouts.

Fixes #4651

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
---
v2 by Vlad:
 - drop void* arithmetics
 - test comment style fixups
 - fix typo in changelog

issue https://github.com/tarantool/tarantool/issues/4651
branch gorcunov/gh-4651-partial-write-2

 src/lib/core/coio_file.c | 62 +++++++++++++++++++++++++++------
 src/lib/core/errinj.h    |  1 +
 test/app/fio.result      | 75 ++++++++++++++++++++++++++++++++++++++++
 test/app/fio.test.lua    | 23 ++++++++++++
 test/box/errinj.result   |  1 +
 5 files changed, 151 insertions(+), 11 deletions(-)

diff --git a/src/lib/core/coio_file.c b/src/lib/core/coio_file.c
index e2345567c..0f21380c5 100644
--- a/src/lib/core/coio_file.c
+++ b/src/lib/core/coio_file.c
@@ -164,10 +164,30 @@ coio_file_close(int fd)
 ssize_t
 coio_pwrite(int fd, const void *buf, size_t count, off_t offset)
 {
-	INIT_COEIO_FILE(eio);
-	eio_req *req = eio_write(fd, (void *) buf, count, offset,
-				 0, coio_complete, &eio);
-	return coio_wait_done(req, &eio);
+	ssize_t left = count, pos = 0, res, chunk;
+	eio_req *req;
+
+	while (left > 0) {
+		INIT_COEIO_FILE(eio);
+		chunk = left;
+
+		ERROR_INJECT(ERRINJ_COIO_WRITE_CHUNK, {
+			chunk = 1;
+		});
+
+		req = eio_write(fd, (char *)buf + pos, chunk,
+				offset + pos, EIO_PRI_DEFAULT,
+				coio_complete, &eio);
+		res = coio_wait_done(req, &eio);
+		if (res < 0) {
+			pos = -1;
+			break;
+		} else {
+			left -= res;
+			pos += res;
+		}
+	}
+	return pos;
 }
 
 ssize_t
@@ -201,6 +221,11 @@ static void
 coio_do_write(eio_req *req)
 {
 	struct coio_file_task *eio = (struct coio_file_task *)req->data;
+
+	ERROR_INJECT(ERRINJ_COIO_WRITE_CHUNK, {
+		eio->write.count = 1;
+	});
+
 	req->result = write(eio->write.fd, eio->write.buf, eio->write.count);
 	eio->errorno = errno;
 }
@@ -208,13 +233,28 @@ coio_do_write(eio_req *req)
 ssize_t
 coio_write(int fd, const void *buf, size_t count)
 {
-	INIT_COEIO_FILE(eio);
-	eio.write.buf = buf;
-	eio.write.count = count;
-	eio.write.fd = fd;
-	eio_req *req = eio_custom(coio_do_write, 0,
-				  coio_complete, &eio);
-	return coio_wait_done(req, &eio);
+	ssize_t left = count, pos = 0, res;
+	eio_req *req;
+
+	while (left > 0) {
+		INIT_COEIO_FILE(eio);
+
+		eio.write.buf	= (char *)buf + pos;
+		eio.write.count	= left;
+		eio.write.fd	= fd;
+
+		req = eio_custom(coio_do_write, EIO_PRI_DEFAULT,
+				 coio_complete, &eio);
+		res = coio_wait_done(req, &eio);
+		if (res < 0) {
+			pos = -1;
+			break;
+		} else {
+			left -= res;
+			pos += res;
+		}
+	}
+	return pos;
 }
 
 static void
diff --git a/src/lib/core/errinj.h b/src/lib/core/errinj.h
index 79073f529..261ab22a8 100644
--- a/src/lib/core/errinj.h
+++ b/src/lib/core/errinj.h
@@ -145,6 +145,7 @@ struct errinj {
 	_(ERRINJ_VY_WRITE_ITERATOR_START_FAIL, ERRINJ_BOOL, {.bparam = false})\
 	_(ERRINJ_VY_RUN_OPEN, ERRINJ_INT, {.iparam = -1})\
 	_(ERRINJ_AUTO_UPGRADE, ERRINJ_BOOL, {.bparam = false})\
+	_(ERRINJ_COIO_WRITE_CHUNK, ERRINJ_BOOL, {.bparam = false}) \
 
 ENUM0(errinj_id, ERRINJ_LIST);
 extern struct errinj errinjs[];
diff --git a/test/app/fio.result b/test/app/fio.result
index 783fa4fab..8a08755a2 100644
--- a/test/app/fio.result
+++ b/test/app/fio.result
@@ -776,6 +776,12 @@ file5 = fio.pathjoin(tree, 'file.5')
 file6 = fio.pathjoin(tree, 'file.6')
 ---
 ...
+file7 = fio.pathjoin(tree, 'file.7')
+---
+...
+file8 = fio.pathjoin(tree, 'file.8')
+---
+...
 fh1 = fio.open(file1, { 'O_RDWR', 'O_TRUNC', 'O_CREAT' }, tonumber('0777', 8))
 ---
 ...
@@ -865,6 +871,75 @@ fh6:close()
 ---
 - true
 ...
+--
+-- gh-4651: Test partial write/pwrite via one byte transfer.
+--
+fh7 = fio.open(file7, { 'O_RDWR', 'O_TRUNC', 'O_CREAT' }, tonumber('0644', 8))
+---
+...
+errinj.set('ERRINJ_COIO_WRITE_CHUNK', true)
+---
+- ok
+...
+fh7:write("one byte transfer, write")
+---
+- true
+...
+errinj.set('ERRINJ_COIO_WRITE_CHUNK', false)
+---
+- ok
+...
+fh7:seek(0)
+---
+- 0
+...
+fh7:read()
+---
+- one byte transfer, write
+...
+fh7:close()
+---
+- true
+...
+fh8 = fio.open(file8, { 'O_RDWR', 'O_TRUNC', 'O_CREAT' }, tonumber('0644', 8))
+---
+...
+errinj.set('ERRINJ_COIO_WRITE_CHUNK', true)
+---
+- ok
+...
+fh8:pwrite("one byte transfer, ", 0)
+---
+- true
+...
+fh8:seek(0)
+---
+- 0
+...
+fh8:read()
+---
+- 'one byte transfer, '
+...
+fh8:pwrite("pwrite", 19)
+---
+- true
+...
+errinj.set('ERRINJ_COIO_WRITE_CHUNK', false)
+---
+- ok
+...
+fh8:seek(0)
+---
+- 0
+...
+fh8:read()
+---
+- one byte transfer, pwrite
+...
+fh8:close()
+---
+- true
+...
 res, err = fio.copyfile(fio.pathjoin(tmp1, 'not_exists.txt'), tmp1)
 ---
 ...
diff --git a/test/app/fio.test.lua b/test/app/fio.test.lua
index 6825b882f..92ba3ff20 100644
--- a/test/app/fio.test.lua
+++ b/test/app/fio.test.lua
@@ -251,6 +251,8 @@ file3 = fio.pathjoin(tree, 'file.3')
 file4 = fio.pathjoin(tree, 'file.4')
 file5 = fio.pathjoin(tree, 'file.5')
 file6 = fio.pathjoin(tree, 'file.6')
+file7 = fio.pathjoin(tree, 'file.7')
+file8 = fio.pathjoin(tree, 'file.8')
 
 fh1 = fio.open(file1, { 'O_RDWR', 'O_TRUNC', 'O_CREAT' }, tonumber('0777', 8))
 fh1:write("gogo")
@@ -280,6 +282,27 @@ fh6:seek(0)
 fh6:read()
 fh6:close()
 
+--
+-- gh-4651: Test partial write/pwrite via one byte transfer.
+--
+fh7 = fio.open(file7, { 'O_RDWR', 'O_TRUNC', 'O_CREAT' }, tonumber('0644', 8))
+errinj.set('ERRINJ_COIO_WRITE_CHUNK', true)
+fh7:write("one byte transfer, write")
+errinj.set('ERRINJ_COIO_WRITE_CHUNK', false)
+fh7:seek(0)
+fh7:read()
+fh7:close()
+fh8 = fio.open(file8, { 'O_RDWR', 'O_TRUNC', 'O_CREAT' }, tonumber('0644', 8))
+errinj.set('ERRINJ_COIO_WRITE_CHUNK', true)
+fh8:pwrite("one byte transfer, ", 0)
+fh8:seek(0)
+fh8:read()
+fh8:pwrite("pwrite", 19)
+errinj.set('ERRINJ_COIO_WRITE_CHUNK', false)
+fh8:seek(0)
+fh8:read()
+fh8:close()
+
 res, err = fio.copyfile(fio.pathjoin(tmp1, 'not_exists.txt'), tmp1)
 res
 err:match("failed to copy") ~= nil
diff --git a/test/box/errinj.result b/test/box/errinj.result
index a066bc4bc..1166f2b30 100644
--- a/test/box/errinj.result
+++ b/test/box/errinj.result
@@ -48,6 +48,7 @@ evals
   - ERRINJ_BUILD_INDEX_DELAY: false
   - ERRINJ_CHECK_FORMAT_DELAY: false
   - ERRINJ_COIO_SENDFILE_CHUNK: -1
+  - ERRINJ_COIO_WRITE_CHUNK: false
   - ERRINJ_DYN_MODULE_COUNT: 0
   - ERRINJ_FIBER_MADVISE: false
   - ERRINJ_FIBER_MPROTECT: -1
-- 
2.26.2