February 2015 - kernelnewbies@kernelnewbies.org

Get Mount target from path
by manty kuma Feb. 5, 2015

Feb. 5, 2015

Hi All, I would like to know the mount target for a given directory. In kernel, is there an API to get the information? Ex: /system/bin -> /system /system/bin is a directory its mount partition is /system. Similarly, I would like to get the target for a given path(Parsing is not right as a target can be mounted to anywhere). Best Regards, Sandeep Kumar

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Does CPU set the Referenced bit Memory Management
by Rakhi Hemani Feb. 5, 2015

Feb. 5, 2015

Hi, I want to understand the mechanism by which linux marks a page as referenced. According to the documentation in "Understanding The Linux Virtual Memory Manager" Figure 11.6 and Table 3.1, there is a bit PG_referenced that can be queried to test if the page was accessed. I want to ask if the CPU can/does set that bit. Also, is this bit set on a LLC miss or on a TLB access? Thanks a lot. Please tell me if there are some manuals/other forums I could refer to for this question. -- Rakhi Hemani Phd Scholar Roll Number PhD1207

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Eudyptula challenge submissions (patch versus proof)
by Tolga Ceylan Feb. 4, 2015

Feb. 4, 2015

Quick question about how to submit patches and proofs. Are separate emails OK with this? For example; 1) a "formal" kernel patch submitted via git send-email 2) proof e-mail submitted via replying to the original task email Or should the proof be in the git commit description itself? Cheers, Tolga

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FW: wrapper device driver
by Malte Vesper Feb. 3, 2015

Feb. 3, 2015

________________________________________ From: Malte Vesper Sent: 02 February 2015 21:43 To: riya khanna Subject: RE: wrapper device driver Why don't you implement your wrapper as a userspace library? ________________________________________ From: kernelnewbies-bounces(a)kernelnewbies.org [kernelnewbies-bounces(a)kernelnewbies.org] on behalf of riya khanna [riyakhanna1983(a)gmail.com] Sent: 02 February 2015 21:24 To: kernelnewbies Subject: wrapper device driver Hi, I'm writing a device driver to to provide a wrapper device around a real device. Is it acceptable to do the following: wrapper_dev_open(flags) { // do additional bookkeeping real_dev_filp = filp_open(real_device_node_path, flags); } wrapper_dev_mmap(mmap_parameters) { // do additional checks return real_dev_filp->f_op->mmap(mmap_parameters); } wrapper_dev_ioctl(ioctl_parameters) { // do additional checks return real_dev_filp->f_op->ioctl(ioctl_parameters); } Is it safe to do something like this? what would be the caveats? Given a good use case, would the maintainers be willing to mainstream something like this? Thanks! -Riya _______________________________________________ Kernelnewbies mailing list Kernelnewbies(a)kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

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Propper use of pci_map_sg
by Malte Vesper Feb. 3, 2015

Feb. 3, 2015

Hi, I am trying to use pci_map_sg in combination with get_user_pages_fast for a driver. However my code screws the processes memory map over. For easier testing I bundled the piinin/unpinning and mapping unmapping into one ioctl call. The following code misses all the checks on return values, since it is only inteneded as a MWE. When I run my code I get a "*BUG: Bad page map in process ...*", after "Done" is printed. I tried following DMA-API-howto.txt and looking at other code, but I fail to see where I go wrong. Regards, Ted Code from the IOCTL handler: case IOCTL_FPGA_PIN_PAGE: { struct pageInfo pageInfo; dev_dbg(&pcidev->dev, pr_fmt("IOCTL: IOCTL_FPGA_PIN_PAGE\n")); if(!copy_from_user(&pageInfo, (void*)arg, sizeof(struct pageInfo))) { //horrible test const int noPages = pageInfo.size/PAGE_SIZE; int pinned; int mapped = 0; struct scatterlist* scatterlist; printk("Test start\n"); //userspacestartpointer, nopages, write?, page* array struct page** pages=kmalloc(sizeof(struct page*)*noPages, GFP_KERNEL); pinned=*get_user_pages_fast*((unsigned long)pageInfo.start, noPages, 1, pages); scatterlist = kmalloc(sizeof(struct scatterlist)*pinned, GFP_KERNEL); for(int i=0; i<pinned; ++i) { sg_set_page(&scatterlist[i], pages[i], PAGE_SIZE, 0); } mapped =*pci_map_sg*(pcidev, scatterlist, pinned, DMA_BIDIRECTIONAL); *pci_unmap_sg*(pcidev, scatterlist, pinned, DMA_BIDIRECTIONAL); for(int i=0; i<pinned; ++i) { *put_page*(pages[i]); //I did place a print here and got two pages unpinned as I expected } kfree(scatterlist); kfree(pages); printk("Done\n"); /*pageInfo.pageId = getPageId(getArea(&pageInfo)); copy_to_user((void*)arg, &pageInfo, sizeof(struct pageInfo));*/ return pageInfo.pageId; } else { return -EFAULT; } } break; P.S.: I used the following code to allocate the memory in userspace, and I use chunk and chunksize to fill pageInfo.start and pageInfo.size respectivly: const int pagesize = sysconf(_SC_PAGESIZE); const int chunksize = 2*pagesize; void* chunk; if(int error = posix_memalign(&chunk, pagesize, chunksize)) { std::cout << "Could not get a page." << std::endl; return error; }

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Zram not working on a different Android version
by Leandro M Barbosa Feb. 3, 2015

Feb. 3, 2015

Hello all, I'm testing zram on Android. Testing using stock kitkat (Android 4.4.2) version in a Samsung S4 went well and I was able to make modifications and use my modified kernel on it just fine, as well as using a custom compiled unmodified version. I then, installed Cyanogenmod (Android 4.4.4) and installed a custom compiled unmodified kernel version in it. However, running the same benchmark tests that I ran for the stock version didn't make zram get pages. I was able to use about 70% or more memory and no swap spaced was used. I'm checking /sys/block/zram0/mem_used_total (and related) and /proc/swaps. There seem to be no difference between the two test scenarios. I made tests using the same compiled kernels in both Android version with the same results: works on stock, does not work on Cyanogenmod. I tried to reach the xda-developers to no avail. There must be some runtime kernel configuration differences between the two scenarios. Anyone able to point me towards the right direction? Thanks in advance. -- Leandro Moreira Barbosa

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why is "const u32 (*tab)[256]" not kerneldoc-able?
by Robert P. J. Day Feb. 3, 2015

Feb. 3, 2015

when generating the kerneldoc manual kernel-api.html with "make htmldocs", the two routines in lib/crc32.c that refer to a parameter of type "const u32 (*tab)[256]" generate kerneldoc errors: Warning(.//lib/crc32.c:148): No description found for parameter 'tab)[256]' Warning(.//lib/crc32.c:148): Excess function parameter 'tab' description in 'crc32_le_generic' Warning(.//lib/crc32.c:293): No description found for parameter 'tab)[256]' Warning(.//lib/crc32.c:293): Excess function parameter 'tab' description in 'crc32_be_generic' Warning(.//lib/crc32.c): no structured comments found kerneldoc content and declaration for one of them: /** * crc32_le_generic() - Calculate bitwise little-endian Ethernet AUTODIN II * CRC32/CRC32C * @crc: seed value for computation. ~0 for Ethernet, sometimes 0 for other * uses, or the previous crc32/crc32c value if computing incrementally. * @p: pointer to buffer over which CRC32/CRC32C is run * @len: length of buffer @p * @tab: little-endian Ethernet table * @polynomial: CRC32/CRC32c LE polynomial */ static inline u32 __pure crc32_le_generic(u32 crc, unsigned char const *p, size_t len, const u32 (*tab)[256], u32 polynomial) { ... snip ... so what is it about that declaration that causes kerneldoc to choke? and because those two routines are the only kerneldoc content in that source file, the kernel-api page generated for that file is just a dummy page, reporting an error. thoughts? rday -- ======================================================================== Robert P. J. Day Ottawa, Ontario, CANADA http://crashcourse.ca Twitter: http://twitter.com/rpjday LinkedIn: http://ca.linkedin.com/in/rpjday ========================================================================

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[PATCH][kerneldoc] Remove non-functional DocBook "!D" tag
by Robert P. J. Day Feb. 3, 2015

Feb. 3, 2015

Remove the description of the apparently long non-functional "!D" kerneldoc directive, and the single place under DocBook that refers to it, which is simply commented out, anyway. If someone someday wants to make that directive functional, then a description of it can be added back in. Signed-off-by: Robert P. J. Day <rpjday(a)crashcourse.ca> --- the warning that "!D" functionality is "not perfect" goes back to 2008, so it's fairly clear that no one is going to miss it. diff --git a/Documentation/DocBook/networking.tmpl b/Documentation/DocBook/networking.tmpl index 29df250..1c9c07a 100644 --- a/Documentation/DocBook/networking.tmpl +++ b/Documentation/DocBook/networking.tmpl @@ -61,9 +61,6 @@ !Enet/core/gen_estimator.c </sect1> <sect1><title>SUN RPC subsystem</title> - !Enet/sunrpc/xdr.c !Enet/sunrpc/svc_xprt.c !Enet/sunrpc/xprt.c diff --git a/Documentation/kernel-doc-nano-HOWTO.txt b/Documentation/kernel-doc-nano-HOWTO.txt index acbc1a3..12f2c57 100644 --- a/Documentation/kernel-doc-nano-HOWTO.txt +++ b/Documentation/kernel-doc-nano-HOWTO.txt @@ -343,9 +343,6 @@ collected from files listed in Documentation/DocBook/Makefile. !I<filename> is replaced by the documentation for functions that are _not_ exported using EXPORT_SYMBOL. -!D<filename> is used to name additional files to search for functions -exported using EXPORT_SYMBOL. - !F<filename> <function [functions...]> is replaced by the documentation, in <filename>, for the functions listed. -- ======================================================================== Robert P. J. Day Ottawa, Ontario, CANADA http://crashcourse.ca Twitter: http://twitter.com/rpjday LinkedIn: http://ca.linkedin.com/in/rpjday ========================================================================

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any plans to generate the DocBook manual for open firmware?
by Robert P. J. Day Feb. 3, 2015

Feb. 3, 2015

just noticed that there is no Doc/DocBook manual in the kernel source tree that covers the set of open firmware (of_*) calls. i can see that *some* of the routines under drivers/of have associated kerneldoc documentation, but there appears to be no DocBook manual that incorporates any of it. anyone know if there's a plan to develop an OF doc some day? or should i start that on my own? :-) rday -- ======================================================================== Robert P. J. Day Ottawa, Ontario, CANADA http://crashcourse.ca Twitter: http://twitter.com/rpjday LinkedIn: http://ca.linkedin.com/in/rpjday ========================================================================

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Running into a problem compilation an application on linux.
by Omkar Houddin Feb. 3, 2015

Feb. 3, 2015

I was trying to compile an application on porteus linux gcc -Wall -O xyz.c -lpci -o xyz /usr/lib/gcc/i486-slackware-linux/4.8.2/../../../../i486-slackware-linux/bin/ld: cannot find -lpci collect2: error ld returned 1 exit status Can you please help me resolve this. Thanks, OMK

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