On Tue, Feb 12, 2013 at 9:24 AM, Chetan Nanda <chetannanda@xxxxxxxxx> wrote: > > > > On Mon, Feb 11, 2013 at 5:25 PM, anish singh <anish198519851985@xxxxxxxxx> wrote: >> >> >> >> On Mon, Feb 11, 2013 at 4:51 PM, पारस <beparas@xxxxxxxxx> wrote: >> > Hi All, >> > >> > To read/write data to user-space from kernel-space we use copy_from_user() >> > and copy_to_user() functions. >> > >> > What is the use of these function? >> > Why kernel can't directly access user address and read/write on to it? >> what will happen if the user space process gets scheduled out while >> you were using it? >> > copy_to/from_user should always be called from process context. So even if a process is scheduled out there is >not impact, as when process schedule back in copying will resume to/from correct page. because page fault will be triggered and the user space will be swapped in. That answers the original question. >> >> > Can any one explain why kernel can't directly access the user-space address. >> > >> > Thanks >> > >> > >> > _______________________________________________ >> > Kernelnewbies mailing list >> > Kernelnewbies@xxxxxxxxxxxxxxxxx >> > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >> > >> >> >> _______________________________________________ >> Kernelnewbies mailing list >> Kernelnewbies@xxxxxxxxxxxxxxxxx >> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >> > _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
