On 8/20/2014 2:33 AM, Rohan Puri wrote: > On Tue, Aug 19, 2014 at 10:04 PM, Loris Degioanni <loris@xxxxxxxxxx> wrote: >> Sure, here's some more context. >> >> I'm one of the developers of sysdig (www.sysdig.org), a tool that >> captures system calls and uses them to offer advanced system monitoring. >> One of the features that our diver offers is the tcpdump-derived concept >> of "snaplen": when a system call with a buffer is captured, it's >> possible to choose how many bytes of that buffer are copied to the >> driver capture buffer. This makes it possible to tune buffer utilization >> and CPU usage vs completeness of data. >> >> Since this feature is important and heavily used, I'd like to extend it >> so that the user has per-fd-type snaplen control. A typical use case is: >> "I want 1000 bytes of each socket buffer, because I'm interested in >> looking at protocol activity, but I don't care about files and so I'm ok >> with just 20 bytes from them". In order for this feature to be useful, >> it needs to be very fast: we use tracepoints to capture system calls, so >> we slow down the original process if we take too long. >> >> And since I'm here, let me expand my question. Another useful thing to >> do would be per-filename snaplen. Use case: "I want the whole content of >> reads and writes to files that are in /etc, but I want only 20 bytes >> from any other system call". This would I guess involve unpacking the >> file structure and retrieving the full file name. Is there any way to do >> it safely and efficiently? >> >> Thanks, >> Loris >> >> >> On 8/19/2014 9:02 AM, Valdis.Kletnieks@xxxxxx wrote: >>> On Tue, 19 Aug 2014 08:38:24 -0700, Loris Degioanni said: >>> >>>> I'm looking for an efficient way to determine the type of an fd (file, >>>> socket...) given its number, from a kernel module. >>> What problem are you trying to solve here? There may be a better API for >>> your problem. So step back - what are you trying to accomplish? >> >> _______________________________________________ >> Kernelnewbies mailing list >> Kernelnewbies@xxxxxxxxxxxxxxxxx >> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > Hi Loris, > > You can get the file type from the fd by doing something like this : - > > struct file *file = fget(fd); > if(!file) > return error; > assert(file->f_inode != NULL); > file_type = (file->f_inode->i_mode & S_IFMT) >> 12; > > Also, you can make use of S_IS*(mode) macros, to check for file types. > > NOTE: fget() makes use of current process's file_struct. > > Regards, > - Rohan Thanks Rohan, and for kernels more recent than 3.14 I assume I need to use fdget instead of fget, right? Loris _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
