From edcda4c08ac033f40a91cb4def2fd0fa35a760ca Mon Sep 17 00:00:00 2001 From: Adhemerval Zanella Date: Wed, 24 Jul 2019 13:48:12 -0300 Subject: mips: Do not malloc on getdents64 fallback This patch changes how the fallback getdents64 implementation calls non-LFS getdents by replacing the scratch_buffer with static buffer plus a loop on getdents calls. This avoids the potential malloc call on scratch_buffer_set_array_size for large input buffer size at the cost of more getdents syscalls. It also adds a small optimization for older kernels, where the first ENOSYS failure for getdents64 disable subsequent calls. Check the dirent tests on a mips64-linux-gnu with getdents64 code disabled. * sysdeps/unix/sysv/linux/mips/mips64/getdents64.c (__getdents64): Add small optimization for older kernel to avoid issuing __NR_getdents64 on each call and replace scratch_buffer usage with a static allocated buffer. Reviewed-by: Florian Weimer --- ChangeLog | 7 ++ sysdeps/unix/sysv/linux/mips/mips64/getdents64.c | 140 +++++++++++++---------- 2 files changed, 88 insertions(+), 59 deletions(-) diff --git a/ChangeLog b/ChangeLog index fa343ed..1d4f418 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,10 @@ +2019-10-09 Adhemerval Zanella + + * sysdeps/unix/sysv/linux/mips/mips64/getdents64.c (__getdents64): + Add small optimization for older kernel to avoid issuing + __NR_getdents64 on each call and replace scratch_buffer usage with + a static allocated buffer. + 2019-10-09 Florian Weimer * config.h.in (HAVE_GCC_GOTDATA): Remove. diff --git a/sysdeps/unix/sysv/linux/mips/mips64/getdents64.c b/sysdeps/unix/sysv/linux/mips/mips64/getdents64.c index a8c65cc..50f5d69 100644 --- a/sysdeps/unix/sysv/linux/mips/mips64/getdents64.c +++ b/sysdeps/unix/sysv/linux/mips/mips64/getdents64.c @@ -22,98 +22,120 @@ #include #include #include -#include #include +#include + ssize_t -__getdents64 (int fd, void *buf0, size_t nbytes) +__getdents64 (int fd, void *buf, size_t nbytes) { - char *buf = buf0; - /* The system call takes an unsigned int argument, and some length checks in the kernel use an int type. */ if (nbytes > INT_MAX) nbytes = INT_MAX; #ifdef __NR_getdents64 - ssize_t ret = INLINE_SYSCALL_CALL (getdents64, fd, buf, nbytes); - if (ret != -1) - return ret; + static int getdents64_supported = true; + if (atomic_load_relaxed (&getdents64_supported)) + { + ssize_t ret = INLINE_SYSCALL_CALL (getdents64, fd, buf, nbytes); + if (ret >= 0 || errno != ENOSYS) + return ret; + + atomic_store_relaxed (&getdents64_supported, false); + } #endif /* Unfortunately getdents64 was only wire-up for MIPS n64 on Linux 3.10. - If syscall is not available it need to fallback to non-LFS one. */ + If the syscall is not available it need to fallback to the non-LFS one. + Also to avoid an unbounded allocation through VLA/alloca or malloc (which + would make the syscall non async-signal-safe) it uses a limited buffer. + This is sub-optimal for large NBYTES, however this is a fallback + mechanism to emulate a syscall that kernel should provide. */ struct kernel_dirent - { - unsigned long d_ino; - unsigned long d_off; - unsigned short int d_reclen; - char d_name[256]; - }; + { +#if _MIPS_SIM == _ABI64 + uint64_t d_ino; + uint64_t d_off; +#else + uint32_t d_ino; + uint32_t d_off; +#endif + unsigned short int d_reclen; + char d_name[1]; + }; + + /* The largest possible practical length of the d_name member are 255 + Unicode characters in UTF-8 encoding, so d_name is 766 bytes long, plus + 18 (mips64) / 10 (mips64n32) bytes from header, for total of 784 (mips64) + / 776 (mips64n32) bytes total. Ensure that the minimum size holds at + least one entry. */ + enum { KBUF_SIZE = 1024 }; + char kbuf[KBUF_SIZE]; + size_t kbuf_size = nbytes < KBUF_SIZE ? nbytes : KBUF_SIZE; const size_t size_diff = (offsetof (struct dirent64, d_name) - offsetof (struct kernel_dirent, d_name)); - size_t red_nbytes = MIN (nbytes - - ((nbytes / (offsetof (struct dirent64, d_name) - + 14)) * size_diff), - nbytes - size_diff); + struct dirent64 *dp = (struct dirent64 *) buf; - struct scratch_buffer tmpbuf; - scratch_buffer_init (&tmpbuf); - if (!scratch_buffer_set_array_size (&tmpbuf, red_nbytes, sizeof (uint8_t))) - INLINE_SYSCALL_ERROR_RETURN_VALUE (ENOMEM); + size_t nb = 0; + off64_t last_offset = -1; - struct kernel_dirent *skdp, *kdp; - skdp = kdp = tmpbuf.data; + ssize_t r = INLINE_SYSCALL_CALL (getdents, fd, kbuf, kbuf_size); + if (r <= 0) + return r; - ssize_t retval = INLINE_SYSCALL_CALL (getdents, fd, kdp, red_nbytes); - if (retval == -1) - { - scratch_buffer_free (&tmpbuf); - return -1; - } + struct kernel_dirent *skdp, *kdp; + skdp = kdp = (struct kernel_dirent *) kbuf; - off64_t last_offset = -1; - struct dirent64 *dp = (struct dirent64 *) buf; - while ((char *) kdp < (char *) skdp + retval) + while ((char *) kdp < (char *) skdp + r) { - const size_t alignment = _Alignof (struct dirent64); - /* Since kdp->d_reclen is already aligned for the kernel structure - this may compute a value that is bigger than necessary. */ - size_t new_reclen = ((kdp->d_reclen + size_diff + alignment - 1) - & ~(alignment - 1)); - if ((char *) dp + new_reclen > buf + nbytes) - { - /* Our heuristic failed. We read too many entries. Reset - the stream. */ - assert (last_offset != -1); - __lseek64 (fd, last_offset, SEEK_SET); - - if ((char *) dp == buf) + /* This macro is used to avoid aliasing violation. */ +#define KDP_MEMBER(src, member) \ + (__typeof__((struct kernel_dirent){0}.member) *) \ + memcpy (&((__typeof__((struct kernel_dirent){0}.member)){0}), \ + ((char *)(src) + offsetof (struct kernel_dirent, member)),\ + sizeof ((struct kernel_dirent){0}.member)) + + /* This is a conservative approximation, since some of size_diff might + fit into the existing padding for alignment. */ + unsigned short int k_reclen = *KDP_MEMBER (kdp, d_reclen); + unsigned short int new_reclen = ALIGN_UP (k_reclen + size_diff, + _Alignof (struct dirent64)); + if (nb + new_reclen > nbytes) + { + /* Entry is too large for the fixed-size buffer. */ + if (last_offset == -1) { - scratch_buffer_free (&tmpbuf); - return INLINE_SYSCALL_ERROR_RETURN_VALUE (EINVAL); + __set_errno (EINVAL); + return -1; } - break; + /* The new entry will overflow the input buffer, rewind to last + obtained entry and return. */ + __lseek64 (fd, last_offset, SEEK_SET); + return (char *) dp - (char *) buf; } - - last_offset = kdp->d_off; - dp->d_ino = kdp->d_ino; - dp->d_off = kdp->d_off; - dp->d_reclen = new_reclen; - dp->d_type = *((char *) kdp + kdp->d_reclen - 1); + nb += new_reclen; + + memcpy (((char *) dp + offsetof (struct dirent64, d_ino)), + KDP_MEMBER (kdp, d_ino), sizeof ((struct dirent64){0}.d_ino)); + memcpy (((char *) dp + offsetof (struct dirent64, d_off)), + KDP_MEMBER (kdp, d_off), sizeof ((struct dirent64){0}.d_off)); + last_offset = *KDP_MEMBER (kdp, d_off); + memcpy (((char *) dp + offsetof (struct dirent64, d_reclen)), + &new_reclen, sizeof (new_reclen)); + dp->d_type = *((char *) kdp + k_reclen - 1); memcpy (dp->d_name, kdp->d_name, - kdp->d_reclen - offsetof (struct kernel_dirent, d_name)); + k_reclen - offsetof (struct kernel_dirent, d_name)); dp = (struct dirent64 *) ((char *) dp + new_reclen); - kdp = (struct kernel_dirent *) (((char *) kdp) + kdp->d_reclen); + kdp = (struct kernel_dirent *) (((char *) kdp) + k_reclen); } - scratch_buffer_free (&tmpbuf); - return (char *) dp - buf; + return (char *) dp - (char *) buf; } libc_hidden_def (__getdents64) weak_alias (__getdents64, getdents64) -- cgit v1.1