From: Herbert Xu <herbert@gondor.apana.org.au>
To: dash@vger.kernel.org
Subject: [PATCH] redir: Use memfd_create instead of pipe
Date: Sun, 14 Apr 2024 15:51:37 +0800 [thread overview]
Message-ID: <ZhuLCZfwRfflgv0v@gondor.apana.org.au> (raw)
Use memfd_create(2) instead of pipe(2). With pipe(2), a fork
is required if the amount of data to be written exceeds the pipe
size. This is not the case with memfd_create.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
---
configure.ac | 2 +-
src/eval.c | 3 +--
src/redir.c | 57 ++++++++++++++++++++++++++++++++++------------------
src/redir.h | 1 +
src/system.h | 7 +++++++
5 files changed, 47 insertions(+), 23 deletions(-)
diff --git a/configure.ac b/configure.ac
index 6993364..cb55c3f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -87,7 +87,7 @@ AC_CHECK_DECL([PRIdMAX],,
dnl Checks for library functions.
AC_CHECK_FUNCS(bsearch faccessat getpwnam getrlimit isalpha killpg \
- mempcpy \
+ memfd_create mempcpy \
sigsetmask stpcpy strchrnul strsignal strtod strtoimax \
strtoumax sysconf)
diff --git a/src/eval.c b/src/eval.c
index 978a174..fce5314 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -635,8 +635,7 @@ evalbackcmd(union node *n, struct backcmd *result)
goto out;
}
- if (pipe(pip) < 0)
- sh_error("Pipe call failed");
+ sh_pipe(pip, 0);
jp = makejob(1);
if (forkshell(jp, n, FORK_NOJOB) == 0) {
FORCEINTON;
diff --git a/src/redir.c b/src/redir.c
index bcc81b4..12233be 100644
--- a/src/redir.c
+++ b/src/redir.c
@@ -32,6 +32,7 @@
* SUCH DAMAGE.
*/
+#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/param.h> /* PIPE_BUF */
@@ -280,6 +281,17 @@ ecreate:
sh_open_fail(fname, O_CREAT, EEXIST);
}
+static int sh_dup2(int ofd, int nfd)
+{
+ if (nfd < 0)
+ nfd = dup(ofd);
+ else
+ nfd = dup2(ofd, nfd);
+ if (nfd < 0)
+ sh_error("%d: %s", ofd, strerror(errno));
+
+ return nfd;
+}
#ifdef notyet
static void dupredirect(union node *redir, int f, char memory[10])
@@ -288,7 +300,6 @@ static void dupredirect(union node *redir, int f)
#endif
{
int fd = redir->nfile.fd;
- int err = 0;
#ifdef notyet
memory[fd] = 0;
@@ -301,26 +312,31 @@ static void dupredirect(union node *redir, int f)
memory[fd] = 1;
else
#endif
- if (dup2(f, fd) < 0) {
- err = errno;
- goto err;
- }
+ sh_dup2(f, fd);
return;
}
f = fd;
- } else if (dup2(f, fd) < 0)
- err = errno;
+ } else
+ sh_dup2(f, fd);
close(f);
- if (err < 0)
- goto err;
-
- return;
-
-err:
- sh_error("%d: %s", f, strerror(err));
}
+int sh_pipe(int pip[2], int memfd)
+{
+ if (memfd) {
+ pip[0] = memfd_create("dash", 0);
+ if (pip[0] >= 0) {
+ pip[1] = sh_dup2(pip[0], -1);
+ return 1;
+ }
+ }
+
+ if (pipe(pip) < 0)
+ sh_error("Pipe call failed");
+
+ return 0;
+}
/*
* Handle here documents. Normally we fork off a process to write the
@@ -331,9 +347,10 @@ err:
STATIC int
openhere(union node *redir)
{
- char *p;
- int pip[2];
size_t len = 0;
+ int pip[2];
+ int memfd;
+ char *p;
p = redir->nhere.doc->narg.text;
if (redir->type == NXHERE) {
@@ -341,12 +358,12 @@ openhere(union node *redir)
p = stackblock();
}
- if (pipe(pip) < 0)
- sh_error("Pipe call failed");
-
len = strlen(p);
- if (len <= PIPESIZE) {
+ memfd = sh_pipe(pip, len > PIPESIZE);
+
+ if (memfd || len <= PIPESIZE) {
xwrite(pip[1], p, len);
+ lseek(pip[1], 0, SEEK_SET);
goto out;
}
diff --git a/src/redir.h b/src/redir.h
index 16f5c20..0be5f1a 100644
--- a/src/redir.h
+++ b/src/redir.h
@@ -50,4 +50,5 @@ int redirectsafe(union node *, int);
void unwindredir(struct redirtab *stop);
struct redirtab *pushredir(union node *redir);
int sh_open(const char *pathname, int flags, int mayfail);
+int sh_pipe(int pip[2], int memfd);
diff --git a/src/system.h b/src/system.h
index 007952c..371c64b 100644
--- a/src/system.h
+++ b/src/system.h
@@ -54,6 +54,13 @@ static inline void sigclearmask(void)
#endif
}
+#ifndef HAVE_MEMFD_CREATE
+static inline int memfd_create(const char *name, unsigned int flags)
+{
+ return -1;
+}
+#endif
+
#ifndef HAVE_MEMPCPY
void *mempcpy(void *, const void *, size_t);
#endif
--
2.39.2
--
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
next reply other threads:[~2024-04-14 7:51 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-14 7:51 Herbert Xu [this message]
2024-04-19 21:24 ` [PATCH] redir: Use memfd_create instead of pipe Jilles Tjoelker
2024-04-20 0:15 ` Herbert Xu
2024-04-21 0:33 ` [v2 PATCH] " Herbert Xu
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