= Large File Support =

== Goal description ==

Fix all applications to remove arbitrary file size limits (generally 2GB+), or other large counts such as inode values (see DebianBug:760985 for an example). This implies not slurping or {{{mmap(2)}}}ing large files into memory (as that might exceed the address space), using correct 64-bit types (f.ex. {{{off_t}}} instead of {{{ssize_t}}}, {{{uint64_t}}} instead of {{{int}}}, etc), using the correct 64-bit variants of types such as {{{off_t}}}, {{{fpos_t}}}, {{{ino_t}}}, {{{rlim_t}}}, {{{blkcnt_t}}}, {{{fsblkcnt_t}}}, {{{fsfilcnt_t}}} and any derived structs that have members with those types, using the correct 64-bit variants of system functions (such as {{{open(2)}}} or {{{stat(2)}}}).

Using the correct system interfaces can be done by defining the preprocessor macro as {{{_FILE_OFFSET_BITS=64}}}. For projects using DebianPkg:autoconf, by adding the {{{AC_SYS_LARGEFILE}}} m4 macro. Otherwise the {{{dpkg-buildflags}}} build feature {{{abi=+lfs}}} can be used to set the correct values in the build flags. Note though, that {{{getconf LFS_CFLAGS}}} '''must not''' be used, as it does not support cross-building. Using {{{_FILE_OFFSET_BITS}}} should require no system function renames (for example from {{{open(2)}}} to {{{open64(2)}}}).

DebianPkg:lintian contains a test that can help identify packages that are not LFS-safe, but it cannot guarantee packages that do not emit the tag are LFS-safe, as they might use inappropriate types or code that might incur in OOM conditions, file truncation, or overwrites.

Note also that enabling LFS for shared objects (shared libraries or plugin interfaces) might imply an ABI break, so this should be evaluated carefully. If there is ABI breakage then this can be queued for the next SONAME bump, or otherwise it needs a transition by keeping the current SONAME but the package name needs to be renamed, and the new one conflict with the old one, which can be rather disruptive for upgrades.

== Current status ==

 * [[https://bugs.debian.org/cgi-bin/pkgreport.cgi?which=tag&data=lfs&archive=no|Bugs tagged lfs]]
 * [[https://udd.debian.org/lintian-tag.cgi?tag=binary-file-built-without-LFS-support|Possible issue noticed by Lintian]]
 
== How to help ==

 * Report bugs on packages with arbitrary file size limits
 * Fix bugs tagged lfs.