On Mon, Nov 02, 2020 at 03:32:59PM +0100, Greg Kroah-Hartman wrote: > On Mon, Nov 02, 2020 at 02:08:36PM +0000, Matthew Wilcox wrote: > > On Mon, Nov 02, 2020 at 02:33:43PM +0100, Greg Kroah-Hartman wrote: > > > > Oh, ugh, sysfs_emit() should be able to work on a buffer that isn't > > > > page aligned. Greg, how about this? > > > > > > How can sysfs_emit() be called on a non-page-aligned buffer? It's being > > > used on the buffer that was passed to the sysfs call. > > > > > > And if you are writing multiple values to a single sysfs file output, > > > well, not good... > > > > See shmem_enabled_show() in mm/shmem.c (output at > > /sys/kernel/mm/transparent_hugepage/shmem_enabled on your machine). > > > > I don't claim it's a good interface, but it exists. > > Ok, that's a common pattern for sysfs files, not that bad. > > What's wrong with using sysfs_emit_at()? We want sysfs_emit() to "know" > that the buffer is PAGE_SIZE big, if you try to allow offsets in it, > that defeats the purpose of the check. For someone who's used to C "strings", it's pretty common to do something like: buf += sprintf(buf, "foo "); buf += sprintf(buf, "bar "); sysfs_emit_at instead wants me to do: len += sprintf(buf + len, "foo "); len += sprintf(buf + len, "bar "); I don't see how the code I wrote defeats the check. It checks that the buffer never crosses a PAGE_SIZE boundary, which is equivalently safe.
