* USB file mmap @ 2014-07-07 14:00 Jeshwanth Kumar N K 2014-07-07 16:34 ` Greg KH 0 siblings, 1 reply; 5+ messages in thread From: Jeshwanth Kumar N K @ 2014-07-07 14:00 UTC (permalink / raw) To: kernelnewbies Hello List, I am trying to understand mmap on files residing in USB flash, so can you please give a pointer from where I can start to understand this? I mean how it works, and which part in kernel takes care of it. Thanks -------------- next part -------------- An HTML attachment was scrubbed... URL: http://lists.kernelnewbies.org/pipermail/kernelnewbies/attachments/20140707/858a5303/attachment.html ^ permalink raw reply [flat|nested] 5+ messages in thread
* USB file mmap 2014-07-07 14:00 USB file mmap Jeshwanth Kumar N K @ 2014-07-07 16:34 ` Greg KH 2014-07-07 19:56 ` Jeshwanth Kumar N K 0 siblings, 1 reply; 5+ messages in thread From: Greg KH @ 2014-07-07 16:34 UTC (permalink / raw) To: kernelnewbies On Mon, Jul 07, 2014 at 07:30:07PM +0530, Jeshwanth Kumar N K wrote: > Hello List, > I am trying to understand mmap on files residing in USB flash, so can you > please give a pointer from where I can start to understand this? I mean how it > works, and which part in kernel takes care of it. That's a _huge_ stack you are talking about here involving a vfs, the memory management core, a filesystem, block layer, SCSI, and USB, at the very least. What _exactly_ are you looking to understand here? And where in the code have you looked and need help with? What documents have you read that were unclear? And why do you need this information? greg k-h ^ permalink raw reply [flat|nested] 5+ messages in thread
* USB file mmap 2014-07-07 16:34 ` Greg KH @ 2014-07-07 19:56 ` Jeshwanth Kumar N K 2014-07-07 20:29 ` Greg Kroah-Hartman 0 siblings, 1 reply; 5+ messages in thread From: Jeshwanth Kumar N K @ 2014-07-07 19:56 UTC (permalink / raw) To: kernelnewbies Hi Greg, Thanks for the reply. I recently purchased an mbed board https://mbed.org/platforms/mbed-LPC1768/ (friend recommended) to learn USB Mass storage class. And used OpenLPC usb stack with fatfs example to check how it works (used protocol analyser and stuff, to know whats happening). In that they are reading each buffer, i mean copying buffer (8k) of data to RAM and process it. And other idea I found is using diskio function in openLPC stack to read the data in USB flash (but this is without file system). As a Linux user I knew in Linux we can do mmap easily for a file (with filesystem). So thought of asking from where to start understanding these concepts :). Greg is it OK to ask this question here? Thanks On 07-Jul-2014 10:00 pm, "Greg KH" <greg@kroah.com> wrote: > On Mon, Jul 07, 2014 at 07:30:07PM +0530, Jeshwanth Kumar N K wrote: > > Hello List, > > I am trying to understand mmap on files residing in USB flash, so can you > > please give a pointer from where I can start to understand this? I mean > how it > > works, and which part in kernel takes care of it. > > That's a _huge_ stack you are talking about here involving a vfs, the > memory management core, a filesystem, block layer, SCSI, and USB, at the > very least. > > What _exactly_ are you looking to understand here? And where in the > code have you looked and need help with? What documents have you read > that were unclear? And why do you need this information? > > greg k-h > -------------- next part -------------- An HTML attachment was scrubbed... URL: http://lists.kernelnewbies.org/pipermail/kernelnewbies/attachments/20140708/06775a0d/attachment.html ^ permalink raw reply [flat|nested] 5+ messages in thread
* USB file mmap 2014-07-07 19:56 ` Jeshwanth Kumar N K @ 2014-07-07 20:29 ` Greg Kroah-Hartman 2014-07-07 20:32 ` Greg Kroah-Hartman 0 siblings, 1 reply; 5+ messages in thread From: Greg Kroah-Hartman @ 2014-07-07 20:29 UTC (permalink / raw) To: kernelnewbies On Tue, Jul 08, 2014 at 01:26:26AM +0530, Jeshwanth Kumar N K wrote: > Hi Greg, > > Thanks for the reply. > > I recently purchased an mbed board > https://mbed.org/platforms/mbed-LPC1768/?(friend recommended) to learn > USB Mass storage class. And used OpenLPC usb stack with fatfs example > to check how it works (used protocol analyser and stuff, to know whats > happening). In that they are reading each buffer, i mean copying > buffer (8k) of data to RAM and process it. And other idea I found is > using diskio function in openLPC stack to read the data in USB flash > (but this is without file system). The USB storage protocol does not define a specific filesystem, so you can send "raw" block commands to the device, but that's usually not very interesting. > As a Linux user I knew in Linux we can do mmap easily for a file (with > filesystem). So thought of asking from where to start understanding > these concepts :). mmap on a file on disk is the same as USB flash, a USB storage device is just a SCSI device (a quite complex little device, not a trivial one at all.) As I said, you have a filesystem, block layer, SCSI layer, USB layer, and then the VFS and other stuff going on here. So I'd recommend focusing on one layer at a time, otherwise you will be overwhelmed. good luck, greg k-h ^ permalink raw reply [flat|nested] 5+ messages in thread
* USB file mmap 2014-07-07 20:29 ` Greg Kroah-Hartman @ 2014-07-07 20:32 ` Greg Kroah-Hartman 0 siblings, 0 replies; 5+ messages in thread From: Greg Kroah-Hartman @ 2014-07-07 20:32 UTC (permalink / raw) To: kernelnewbies On Mon, Jul 07, 2014 at 01:29:29PM -0700, Greg Kroah-Hartman wrote: > On Tue, Jul 08, 2014 at 01:26:26AM +0530, Jeshwanth Kumar N K wrote: > > Hi Greg, > > > > Thanks for the reply. > > > > I recently purchased an mbed board > > https://mbed.org/platforms/mbed-LPC1768/?(friend recommended) to learn > > USB Mass storage class. Wait, you mean the USB storage class from the device side, right? If so, just read the USB storage spec, and the SCSI spec that it referrs to. There is no need to worry about mmap, or anything other than "normal" scsi block commands. This device can't run Linux, it's too small, which is a shame, as Linux works really well running as a USB "gadget". good luck, greg k-h ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2014-07-07 20:32 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2014-07-07 14:00 USB file mmap Jeshwanth Kumar N K 2014-07-07 16:34 ` Greg KH 2014-07-07 19:56 ` Jeshwanth Kumar N K 2014-07-07 20:29 ` Greg Kroah-Hartman 2014-07-07 20:32 ` Greg Kroah-Hartman
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