On Wed, Nov 19, 2025 at 04:14:51PM -0800, Gustavo Luiz Duarte wrote: > The userdata buffer in struct netconsole_target is currently statically > allocated with a size of MAX_USERDATA_ITEMS * MAX_EXTRADATA_ENTRY_LEN > (16 * 256 = 4096 bytes). This wastes memory when userdata entries are > not used or when only a few entries are configured, which is common in > typical usage scenarios. It also forces us to keep MAX_USERDATA_ITEMS > small to limit the memory wasted. > > Change the userdata buffer from a static array to a dynamically > allocated pointer. The buffer is now allocated on-demand in > update_userdata() whenever userdata entries are added, modified, or > removed via configfs. The implementation calculates the exact size > needed for all current userdata entries, allocates a new buffer of that > size, formats the entries into it, and atomically swaps it with the old > buffer. > > This approach provides several benefits: > - Memory efficiency: Targets with no userdata use zero bytes instead of > 4KB, and targets with userdata only allocate what they need; > - Scalability: Makes it practical to increase MAX_USERDATA_ITEMS to a > much larger value without imposing a fixed memory cost on every > target; > - No hot-path overhead: Allocation occurs during configuration (write to > configfs), not during message transmission > > If memory allocation fails during userdata update, -ENOMEM is returned > to userspace through the configfs attribute write operation. > > The sysdata buffer remains statically allocated since it has a smaller > fixed size (MAX_SYSDATA_ITEMS * MAX_EXTRADATA_ENTRY_LEN = 4 * 256 = 1024 > bytes) and its content length is less predictable. > > Signed-off-by: Gustavo Luiz Duarte <[email protected]>
Reviewed-by: Breno Leitao <[email protected]>
