How to check if a file descriptor/ memory is mmap able?
I am trying to access a memory location "/dev/xdma_h2c_0". I have achieved the read/write using system read/write functions.
Now I am trying to use mmap to do the same. But I am getting No such device error.
Is there a quick way to tell whether a location/file descriptor is mmap (-able) or not?
(This memory location is available on the Xilinx Virtex FPGA board using the Xilinx drivers)
python
asked Feb 13 at 9:42
user10589957user10589957
31
add a comment |
I am trying to access a memory location "/dev/xdma_h2c_0". I have achieved the read/write using system read/write functions.
Now I am trying to use mmap to do the same. But I am getting No such device error.
Is there a quick way to tell whether a location/file descriptor is mmap (-able) or not?
(This memory location is available on the Xilinx Virtex FPGA board using the Xilinx drivers)
python
asked Feb 13 at 9:42
user10589957user10589957
31
This is a region of memory exposed by the FPGA? Is/dev/xdma_h2c_0a character device or block device? What is the errno?ENODEV/ENOENT? From what you've provided, I'd suggest it isn't, but that doesn't mean you can't potentially improve the driver to make it possible!
– Attie
Feb 13 at 9:48
Yes. It's a character device. Errno as given by python script is "OSError: [Errno 19] No such device". Can you tell from this whether is possible to mmap it?
– user10589957
Feb 13 at 11:29
You cannotmmap()character devices - they aren't seekable, etc...
– Attie
Feb 13 at 18:47
add a comment |
I am trying to access a memory location "/dev/xdma_h2c_0". I have achieved the read/write using system read/write functions.
Now I am trying to use mmap to do the same. But I am getting No such device error.
Is there a quick way to tell whether a location/file descriptor is mmap (-able) or not?
(This memory location is available on the Xilinx Virtex FPGA board using the Xilinx drivers)
python
asked Feb 13 at 9:42
user10589957user10589957
31
I am trying to access a memory location "/dev/xdma_h2c_0". I have achieved the read/write using system read/write functions.
Now I am trying to use mmap to do the same. But I am getting No such device error.
Is there a quick way to tell whether a location/file descriptor is mmap (-able) or not?
(This memory location is available on the Xilinx Virtex FPGA board using the Xilinx drivers)
python
python
asked Feb 13 at 9:42
user10589957user10589957
31
asked Feb 13 at 9:42
user10589957user10589957
31
asked Feb 13 at 9:42
user10589957user10589957
31
asked Feb 13 at 9:42
user10589957user10589957
31
asked Feb 13 at 9:42
user10589957user10589957
31
31
This is a region of memory exposed by the FPGA? Is/dev/xdma_h2c_0a character device or block device? What is the errno?ENODEV/ENOENT? From what you've provided, I'd suggest it isn't, but that doesn't mean you can't potentially improve the driver to make it possible!
– Attie
Feb 13 at 9:48
Yes. It's a character device. Errno as given by python script is "OSError: [Errno 19] No such device". Can you tell from this whether is possible to mmap it?
– user10589957
Feb 13 at 11:29
You cannotmmap()character devices - they aren't seekable, etc...
– Attie
Feb 13 at 18:47
add a comment |
This is a region of memory exposed by the FPGA? Is/dev/xdma_h2c_0a character device or block device? What is the errno?ENODEV/ENOENT? From what you've provided, I'd suggest it isn't, but that doesn't mean you can't potentially improve the driver to make it possible!
– Attie
Feb 13 at 9:48
Yes. It's a character device. Errno as given by python script is "OSError: [Errno 19] No such device". Can you tell from this whether is possible to mmap it?
– user10589957
Feb 13 at 11:29
You cannotmmap()character devices - they aren't seekable, etc...
– Attie
Feb 13 at 18:47
This is a region of memory exposed by the FPGA? Is
/dev/xdma_h2c_0 a character device or block device? What is the errno? ENODEV / ENOENT? From what you've provided, I'd suggest it isn't, but that doesn't mean you can't potentially improve the driver to make it possible!– Attie
Feb 13 at 9:48
This is a region of memory exposed by the FPGA? Is
/dev/xdma_h2c_0 a character device or block device? What is the errno? ENODEV / ENOENT? From what you've provided, I'd suggest it isn't, but that doesn't mean you can't potentially improve the driver to make it possible!– Attie
Feb 13 at 9:48
Yes. It's a character device. Errno as given by python script is "OSError: [Errno 19] No such device". Can you tell from this whether is possible to mmap it?
– user10589957
Feb 13 at 11:29
Yes. It's a character device. Errno as given by python script is "OSError: [Errno 19] No such device". Can you tell from this whether is possible to mmap it?
– user10589957
Feb 13 at 11:29
You cannot
mmap() character devices - they aren't seekable, etc...– Attie
Feb 13 at 18:47
You cannot
mmap() character devices - they aren't seekable, etc...– Attie
Feb 13 at 18:47
add a comment |
1 Answer
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According to your comments, /dev/xdma_h2c_0 is a character device, and thus it is not possible to use mmap() on it - that just makes no sense, primarily because it's not an addressable device (you can't use lseek() / fseek() either).
If the FPGA's address space is presented via PCI / PCIe, then you might have luck with using lspci to locate its memory regions, opening /dev/mem, and using mmap() with that... though this comes with all relevant security concerns and warnings... i.e: don't do this in a real product or outside the lab / home.
More ideally though, you'd write a proper drive to expose whatever functionality you're providing in the FPGA.
According to your follow-up comments, you are able to call lseek() on the device, which is not typical for character devices.
The file_operations structure outlines what "features" are available from the device or node.
Is that because the address space is presented via the Xilinx PCIe drivers?
Looking in the mainline kernel I can't immediately see the driver, but if the interface to the FPGA is indeed PCIe, and there isn't some weird windowing mechanism used, then I would imagine there is some flag region of memory available and therefore a method for seeking within it.
answered Feb 13 at 18:52
AttieAttie
11.7k32845
Thanks for the explanation. Just a small doubt. I can actually lseek() it since that's how I implemented read/write using system functions (os.lseek() then os.read()/os.write() in python). Is that because the address space is presented via the Xilinx PCIe drivers?
– user10589957
Feb 14 at 3:49
Interesting - it's not typically possible to uselseek()on a character device... See my update :-)
– Attie
Feb 14 at 11:14
add a comment |
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According to your comments, /dev/xdma_h2c_0 is a character device, and thus it is not possible to use mmap() on it - that just makes no sense, primarily because it's not an addressable device (you can't use lseek() / fseek() either).
If the FPGA's address space is presented via PCI / PCIe, then you might have luck with using lspci to locate its memory regions, opening /dev/mem, and using mmap() with that... though this comes with all relevant security concerns and warnings... i.e: don't do this in a real product or outside the lab / home.
More ideally though, you'd write a proper drive to expose whatever functionality you're providing in the FPGA.
According to your follow-up comments, you are able to call lseek() on the device, which is not typical for character devices.
The file_operations structure outlines what "features" are available from the device or node.
Is that because the address space is presented via the Xilinx PCIe drivers?
Looking in the mainline kernel I can't immediately see the driver, but if the interface to the FPGA is indeed PCIe, and there isn't some weird windowing mechanism used, then I would imagine there is some flag region of memory available and therefore a method for seeking within it.
answered Feb 13 at 18:52
AttieAttie
11.7k32845
Thanks for the explanation. Just a small doubt. I can actually lseek() it since that's how I implemented read/write using system functions (os.lseek() then os.read()/os.write() in python). Is that because the address space is presented via the Xilinx PCIe drivers?
– user10589957
Feb 14 at 3:49
Interesting - it's not typically possible to uselseek()on a character device... See my update :-)
– Attie
Feb 14 at 11:14
add a comment |
According to your comments, /dev/xdma_h2c_0 is a character device, and thus it is not possible to use mmap() on it - that just makes no sense, primarily because it's not an addressable device (you can't use lseek() / fseek() either).
If the FPGA's address space is presented via PCI / PCIe, then you might have luck with using lspci to locate its memory regions, opening /dev/mem, and using mmap() with that... though this comes with all relevant security concerns and warnings... i.e: don't do this in a real product or outside the lab / home.
More ideally though, you'd write a proper drive to expose whatever functionality you're providing in the FPGA.
According to your follow-up comments, you are able to call lseek() on the device, which is not typical for character devices.
The file_operations structure outlines what "features" are available from the device or node.
Is that because the address space is presented via the Xilinx PCIe drivers?
Looking in the mainline kernel I can't immediately see the driver, but if the interface to the FPGA is indeed PCIe, and there isn't some weird windowing mechanism used, then I would imagine there is some flag region of memory available and therefore a method for seeking within it.
answered Feb 13 at 18:52
AttieAttie
11.7k32845
Thanks for the explanation. Just a small doubt. I can actually lseek() it since that's how I implemented read/write using system functions (os.lseek() then os.read()/os.write() in python). Is that because the address space is presented via the Xilinx PCIe drivers?
– user10589957
Feb 14 at 3:49
Interesting - it's not typically possible to uselseek()on a character device... See my update :-)
– Attie
Feb 14 at 11:14
add a comment |
According to your comments, /dev/xdma_h2c_0 is a character device, and thus it is not possible to use mmap() on it - that just makes no sense, primarily because it's not an addressable device (you can't use lseek() / fseek() either).
If the FPGA's address space is presented via PCI / PCIe, then you might have luck with using lspci to locate its memory regions, opening /dev/mem, and using mmap() with that... though this comes with all relevant security concerns and warnings... i.e: don't do this in a real product or outside the lab / home.
More ideally though, you'd write a proper drive to expose whatever functionality you're providing in the FPGA.
According to your follow-up comments, you are able to call lseek() on the device, which is not typical for character devices.
The file_operations structure outlines what "features" are available from the device or node.
Is that because the address space is presented via the Xilinx PCIe drivers?
Looking in the mainline kernel I can't immediately see the driver, but if the interface to the FPGA is indeed PCIe, and there isn't some weird windowing mechanism used, then I would imagine there is some flag region of memory available and therefore a method for seeking within it.
answered Feb 13 at 18:52
AttieAttie
11.7k32845
According to your comments, /dev/xdma_h2c_0 is a character device, and thus it is not possible to use mmap() on it - that just makes no sense, primarily because it's not an addressable device (you can't use lseek() / fseek() either).
If the FPGA's address space is presented via PCI / PCIe, then you might have luck with using lspci to locate its memory regions, opening /dev/mem, and using mmap() with that... though this comes with all relevant security concerns and warnings... i.e: don't do this in a real product or outside the lab / home.
More ideally though, you'd write a proper drive to expose whatever functionality you're providing in the FPGA.
According to your follow-up comments, you are able to call lseek() on the device, which is not typical for character devices.
The file_operations structure outlines what "features" are available from the device or node.
Is that because the address space is presented via the Xilinx PCIe drivers?
Looking in the mainline kernel I can't immediately see the driver, but if the interface to the FPGA is indeed PCIe, and there isn't some weird windowing mechanism used, then I would imagine there is some flag region of memory available and therefore a method for seeking within it.
answered Feb 13 at 18:52
AttieAttie
11.7k32845
edited Feb 14 at 11:14
answered Feb 13 at 18:52
AttieAttie
11.7k32845
answered Feb 13 at 18:52
AttieAttie
11.7k32845
answered Feb 13 at 18:52
AttieAttie
11.7k32845
11.7k32845
Thanks for the explanation. Just a small doubt. I can actually lseek() it since that's how I implemented read/write using system functions (os.lseek() then os.read()/os.write() in python). Is that because the address space is presented via the Xilinx PCIe drivers?
– user10589957
Feb 14 at 3:49
Interesting - it's not typically possible to uselseek()on a character device... See my update :-)
– Attie
Feb 14 at 11:14
add a comment |
Thanks for the explanation. Just a small doubt. I can actually lseek() it since that's how I implemented read/write using system functions (os.lseek() then os.read()/os.write() in python). Is that because the address space is presented via the Xilinx PCIe drivers?
– user10589957
Feb 14 at 3:49
Interesting - it's not typically possible to uselseek()on a character device... See my update :-)
– Attie
Feb 14 at 11:14
Thanks for the explanation. Just a small doubt. I can actually lseek() it since that's how I implemented read/write using system functions (os.lseek() then os.read()/os.write() in python). Is that because the address space is presented via the Xilinx PCIe drivers?
– user10589957
Feb 14 at 3:49
Thanks for the explanation. Just a small doubt. I can actually lseek() it since that's how I implemented read/write using system functions (os.lseek() then os.read()/os.write() in python). Is that because the address space is presented via the Xilinx PCIe drivers?
– user10589957
Feb 14 at 3:49
Interesting - it's not typically possible to use
lseek() on a character device... See my update :-)– Attie
Feb 14 at 11:14
Interesting - it's not typically possible to use
lseek() on a character device... See my update :-)– Attie
Feb 14 at 11:14
add a comment |
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This is a region of memory exposed by the FPGA? Is
/dev/xdma_h2c_0a character device or block device? What is the errno?ENODEV/ENOENT? From what you've provided, I'd suggest it isn't, but that doesn't mean you can't potentially improve the driver to make it possible!– Attie
Feb 13 at 9:48
Yes. It's a character device. Errno as given by python script is "OSError: [Errno 19] No such device". Can you tell from this whether is possible to mmap it?
– user10589957
Feb 13 at 11:29
You cannot
mmap()character devices - they aren't seekable, etc...– Attie
Feb 13 at 18:47