eal/linux: fix Rx interrupt read error management

In eal_intr_proc_rxtx_intr, negative value may be used as argument to
a function expecting a positive value. If 'read' returns EAGAIN as
example, the bytes_read updates to a negative value which continue
be passed as argument for the next 'read'.

Coverity issue: 107115

Function read(fd, &buf, bytes_read) returns a negative number.
Assigning: signed variable bytes_read = read.
CID 107115 (#1 of 1): Argument cannot be negative
(NEGATIVE_RETURNS) bytes_read is passed to a parameter
that cannot be negative.
    bytes_read = read(fd, &buf, bytes_read);

Fixes: c9f3ec1a0f3f ("eal/linux: add Rx interrupt control function")

Signed-off-by: Cunming Liang <cunming.liang@intel.com>
Acked-by: John McNamara <john.mcnamara@intel.com>
Acked-by: David Marchand <david.marchand@6wind.com>

diff --git a/lib/librte_eal/linuxapp/eal/eal_interrupts.c b/lib/librte_eal/linuxapp/eal/eal_interrupts.c
index 470d6a1..06b26a9 100644 (file)
--- a/lib/librte_eal/linuxapp/eal/eal_interrupts.c
+++ b/lib/librte_eal/linuxapp/eal/eal_interrupts.c
@@ -901,6 +901,7 @@ eal_intr_proc_rxtx_intr(int fd, const struct rte_intr_handle *intr_handle)
 {
        union rte_intr_read_buffer buf;
        int bytes_read = 1;
+       int nbytes;
 
        switch (intr_handle->type) {
        case RTE_INTR_HANDLE_UIO:
@@ -925,15 +926,15 @@ eal_intr_proc_rxtx_intr(int fd, const struct rte_intr_handle *intr_handle)
         * for epoll_wait.
         */
        do {
-               bytes_read = read(fd, &buf, bytes_read);
-               if (bytes_read < 0) {
+               nbytes = read(fd, &buf, bytes_read);
+               if (nbytes < 0) {
                        if (errno == EINTR || errno == EWOULDBLOCK ||
                            errno == EAGAIN)
                                continue;
                        RTE_LOG(ERR, EAL,
                                "Error reading from fd %d: %s\n",
                                fd, strerror(errno));
-               } else if (bytes_read == 0)
+               } else if (nbytes == 0)
                        RTE_LOG(ERR, EAL, "Read nothing from fd %d\n", fd);
                return;
        } while (1);