[PATCH] safe{read,write}: Don't lie on nonblocking FD

[Michal Privoznik <mprivozn@xxxxxxxxxx>]

Currently, whenever somebody calls saferead() on nonblocking FD
(safewrite() is totally interchangeable for purpose of this
message) he might get wrong return value. For instance, in the
first iteration some data is read. The number of bytes read is
stored into local variable 'nread'. However, in next iterations
we can get -1 from read() with errno == EAGAIN, in which case the
-1 is returned despite fact some data has already been read. So
the caller gets confused.

Moreover, the comment just above the functions says, they act
like regular read() with nicer handling of EINTR. Well, they
don't now.
---
 src/util/virutil.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/util/virutil.c b/src/util/virutil.c
index b36e9d3..cd19971 100644
--- a/src/util/virutil.c
+++ b/src/util/virutil.c
@@ -105,6 +105,8 @@ saferead(int fd, void *buf, size_t count)
     size_t nread = 0;
     while (count > 0) {
         ssize_t r = read(fd, buf, count);
+        if (r < 0 && nread && errno == EAGAIN)
+            return nread;
         if (r < 0 && errno == EINTR)
             continue;
         if (r < 0)
@@ -125,7 +127,8 @@ safewrite(int fd, const void *buf, size_t count)
     size_t nwritten = 0;
     while (count > 0) {
         ssize_t r = write(fd, buf, count);
-
+        if (r < 0 && nwritten && errno == EAGAIN)
+            return nwritten;
         if (r < 0 && errno == EINTR)
             continue;
         if (r < 0)
-- 
1.8.0.2

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