Eal:Error reading from file descriptor 33: Input/output error

Problem description

VMWARE In the virtual machine ,82545EM Virtual network card binding igb_uio after , function dpdk Program ,dpdk The program always has the following alarm information ：

Eal:Error reading from file descriptor 33: Input/output error

The use of dpdk Version is 16.04, The procedure is l2fwd.

Problem analysis

1. dpdk Internal code

Code related to error reporting ：

						bytes_read = read(events[n].data.fd, &buf, bytes_read);
                        if (bytes_read < 0) {
    
                                if (errno == EINTR || errno == EWOULDBLOCK)
                                        continue;

                                RTE_LOG(ERR, EAL, "Error reading from file "
                                        "descriptor %d: %s\n",
                                        events[n].data.fd,
                                        strerror(errno));

strerror The result of printing is Input/output error, Inquire about Standard error value table , The relevant return values are defined as follows ：

#define EIO 5 /* I/O error */

Show that the problem is from uio File reading returned EIO Wrong value , So here comes the question EIO Where does this return value come from ？

2. uio The code in the module

uio In the module uio File registration read The code of the callback function is as follows ：

static ssize_t uio_read(struct file *filep, char __user *buf,
                        size_t count, loff_t *ppos)
{
    
        struct uio_listener *listener = filep->private_data;
        struct uio_device *idev = listener->dev;
        DECLARE_WAITQUEUE(wait, current);
        ssize_t retval;
        s32 event_count;

        if (!idev->info->irq)
                return -EIO;

In the above code uio_read It's reading /dev/uioX File is the function finally called in the kernel . As can be seen from the above function logic , When idev->info->irq The value of is 0 Will return to -EIO error .

that idev->info->irq Where was it initialized ？

Research confirms that it is in igb_uio.c Is initialized in .

3. igb_uio.c In the initialization uio_info In structure irq Location of field

The relevant code is as follows ：

switch (igbuio_intr_mode_preferred) {
    
        case RTE_INTR_MODE_MSIX:
                /* Only 1 msi-x vector needed */
                msix_entry.entry = 0;
                if (pci_enable_msix(dev, &msix_entry, 1) == 0) {
    
                        dev_dbg(&dev->dev, "using MSI-X");
                        udev->info.irq = msix_entry.vector;
                        udev->mode = RTE_INTR_MODE_MSIX;
                        break;
                }
                /* fall back to INTX */
        case RTE_INTR_MODE_LEGACY:
                if (pci_intx_mask_supported(dev)) {
    
                        dev_dbg(&dev->dev, "using INTX");
                        udev->info.irq_flags = IRQF_SHARED;
                        udev->info.irq = dev->irq;
                        udev->mode = RTE_INTR_MODE_LEGACY;
                        break;
                }
                dev_notice(&dev->dev, "PCI INTX mask not supported\n");
                /* fall back to no IRQ */
        case RTE_INTR_MODE_NONE:
                udev->mode = RTE_INTR_MODE_NONE;
                udev->info.irq = 0;
                break;

        default:
                dev_err(&dev->dev, "invalid IRQ mode %u",
                        igbuio_intr_mode_preferred);
                err = -EINVAL;
                goto fail_release_iomem;
        }

The above process is based on igb_uio Match the interrupt mode set when the module is loaded , The default value is RTE_INTR_MODE_MSIX, because VMWARE In the environment ,82545EM Network card does not support msic And intx interrupt , The process goes to RTE_INTR_MODE_NONE case in ,irq The value of is set to 0, This leads to dpdk adopt read Read uio There are always errors in the file .

resolvent

Even though VMWARE In the environment 82545EM Virtual network card does not support msix、intx interrupt , however dpdk The program still works , To some extent, it indicates that the function of interrupt part is not used .

At the same time, analyze the code to determine that only lsc interrupt , And we're not right about 82545EM Network card enable lsc interrupt .

Based on the fact that , modify igb_uio Code , It is judged that the network card model is 82545EM execute RTE_INTR_MODE_LEGACY In the process .

The test confirmed that the modified problem was solved .

Another alternative modification is in dpdk pmd Drive for 82545EM The network card does not register to listen uio Interruptions .

The specific modification method is as follows ：

stay eth_em_dev_init Judge the network card model , If 82545EM, The interface pci_dev in intr_handle Of fd Field set to -1.