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[PATCH v2 1/5] mips: Do not malloc on getdents64 fallback
- From: Adhemerval Zanella <adhemerval dot zanella at linaro dot org>
- To: libc-alpha at sourceware dot org
- Date: Wed, 31 Jul 2019 15:31:32 -0300
- Subject: [PATCH v2 1/5] 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.
---
.../unix/sysv/linux/mips/mips64/getdents64.c | 122 ++++++++----------
1 file changed, 54 insertions(+), 68 deletions(-)
diff --git a/sysdeps/unix/sysv/linux/mips/mips64/getdents64.c b/sysdeps/unix/sysv/linux/mips/mips64/getdents64.c
index 8bf3abb0e0..3b5afd9324 100644
--- a/sysdeps/unix/sysv/linux/mips/mips64/getdents64.c
+++ b/sysdeps/unix/sysv/linux/mips/mips64/getdents64.c
@@ -22,98 +22,84 @@
#include <assert.h>
#include <sys/param.h>
#include <unistd.h>
-#include <scratch_buffer.h>
#include <limits.h>
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 bool getdents64_supportted = true;
+ if (atomic_load_relaxed (&getdents64_supportted))
+ {
+ ssize_t ret = INLINE_SYSCALL_CALL (getdents64, fd, buf, nbytes);
+ if (ret >= 0 || errno != ENOSYS)
+ return ret;
+
+ atomic_store_relaxed (&getdents64_supportted, 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. */
+ enum { KBUF_SIZE = 1024 };
struct kernel_dirent
- {
- unsigned long d_ino;
- unsigned long d_off;
- unsigned short int d_reclen;
- char d_name[256];
- };
-
- 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 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);
-
- struct kernel_dirent *skdp, *kdp;
- skdp = kdp = tmpbuf.data;
-
- ssize_t retval = INLINE_SYSCALL_CALL (getdents, fd, kdp, red_nbytes);
- if (retval == -1)
- {
- scratch_buffer_free (&tmpbuf);
- return -1;
- }
+ {
+ unsigned long d_ino;
+ unsigned long d_off;
+ unsigned short int d_reclen;
+ char d_name[1];
+ } kbuf[KBUF_SIZE / sizeof (struct kernel_dirent)];
+ size_t kbuf_size = nbytes < KBUF_SIZE ? nbytes : KBUF_SIZE;
- off64_t last_offset = -1;
struct dirent64 *dp = (struct dirent64 *) buf;
- while ((char *) kdp < (char *) skdp + retval)
+
+ size_t nb = 0;
+ off64_t last_offset = -1;
+
+ ssize_t r;
+ while ((r = INLINE_SYSCALL_CALL (getdents, fd, kbuf, kbuf_size)) > 0)
{
- 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)
+ struct kernel_dirent *skdp, *kdp;
+ skdp = kdp = kbuf;
+
+ while ((char *) kdp < (char *) skdp + r)
+ {
+ const size_t alignment = _Alignof (struct dirent64);
+ size_t new_reclen = ((kdp->d_reclen + alignment - 1)
+ & ~(alignment - 1));
+ if (nb + new_reclen > nbytes)
{
- scratch_buffer_free (&tmpbuf);
- return INLINE_SYSCALL_ERROR_RETURN_VALUE (EINVAL);
+ /* The new entry will overflow the input buffer, rewind to
+ last obtained entry and return. */
+ __lseek64 (fd, last_offset, SEEK_SET);
+ goto out;
}
+ nb += new_reclen;
- break;
- }
-
- 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);
- memcpy (dp->d_name, kdp->d_name,
- kdp->d_reclen - offsetof (struct kernel_dirent, d_name));
+ dp->d_ino = kdp->d_ino;
+ dp->d_off = last_offset = kdp->d_off;
+ dp->d_reclen = new_reclen;
+ dp->d_type = *((char *) kdp + kdp->d_reclen - 1);
+ memcpy (dp->d_name, kdp->d_name,
+ kdp->d_reclen - offsetof (struct kernel_dirent, d_name));
- dp = (struct dirent64 *) ((char *) dp + new_reclen);
- kdp = (struct kernel_dirent *) (((char *) kdp) + kdp->d_reclen);
+ dp = (struct dirent64 *) ((char *) dp + new_reclen);
+ kdp = (struct kernel_dirent *) (((char *) kdp) + kdp->d_reclen);
+ }
}
- scratch_buffer_free (&tmpbuf);
- return (char *) dp - buf;
+out:
+ return (char *) dp - (char *) buf;
}
libc_hidden_def (__getdents64)
weak_alias (__getdents64, getdents64)
--
2.17.1