wrapper.c: add xpread() similar to xread()

It is a common mistake to call read(2)/pread(2) and forget to
anticipate that they may return error with EAGAIN/EINTR when the
system call is interrupted.

We have xread() helper to relieve callers of read(2) from having to
worry about it; add xpread() helper to do the same for pread(2).

Update the caller in the builtin/index-pack.c and the mmap emulation
in compat/.

Signed-off-by: Yiannis Marangos <yiannis.marangos@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/index-pack.c b/builtin/index-pack.c
index 9e9eb4b74e8335f097c7cc9e261b051feda0bf0d..e7a6b537b4b8c9ed4310b25d4a82a14b2a7ea603 100644 (file)
--- a/builtin/index-pack.c
+++ b/builtin/index-pack.c
@@ -542,7 +542,7 @@ static void *unpack_data(struct object_entry *obj,
 
        do {
                ssize_t n = (len < 64*1024) ? len : 64*1024;
-               n = pread(pack_fd, inbuf, n, from);
+               n = xpread(pack_fd, inbuf, n, from);
                if (n < 0)
                        die_errno(_("cannot pread pack file"));
                if (!n)

diff --git a/compat/mmap.c b/compat/mmap.c
index c9d46d174259f42a3e2a2eb073475aba517044be..7f662fef7bcb408045eb1536afed058a607ae97b 100644 (file)
--- a/compat/mmap.c
+++ b/compat/mmap.c
@@ -14,7 +14,7 @@ void *git_mmap(void *start, size_t length, int prot, int flags, int fd, off_t of
        }
 
        while (n < length) {
-               ssize_t count = pread(fd, (char *)start + n, length - n, offset + n);
+               ssize_t count = xpread(fd, (char *)start + n, length - n, offset + n);
 
                if (count == 0) {
                        memset((char *)start+n, 0, length-n);
@@ -22,8 +22,6 @@ void *git_mmap(void *start, size_t length, int prot, int flags, int fd, off_t of
                }
 
                if (count < 0) {
-                       if (errno == EAGAIN || errno == EINTR)
-                               continue;
                        free(start);
                        errno = EACCES;
                        return MAP_FAILED;

diff --git a/git-compat-util.h b/git-compat-util.h
index 7776f126d3bd4facfe987bd844a339c8a17b102a..9eec5fb52b6fc8289c2e7d1dc01625b69c55f18f 100644 (file)
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -534,6 +534,7 @@ extern void *xcalloc(size_t nmemb, size_t size);
 extern void *xmmap(void *start, size_t length, int prot, int flags, int fd, off_t offset);
 extern ssize_t xread(int fd, void *buf, size_t len);
 extern ssize_t xwrite(int fd, const void *buf, size_t len);
+extern ssize_t xpread(int fd, void *buf, size_t len, off_t offset);
 extern int xdup(int fd);
 extern FILE *xfdopen(int fd, const char *mode);
 extern int xmkstemp(char *template);

diff --git a/wrapper.c b/wrapper.c
index 0cc56368bd8ccef90ff643ce091cae25007eeee7..5b3c7fceb34c0aff6b1b798070b068bf71ed6b3f 100644 (file)
--- a/wrapper.c
+++ b/wrapper.c
@@ -174,6 +174,24 @@ ssize_t xwrite(int fd, const void *buf, size_t len)
        }
 }
 
+/*
+ * xpread() is the same as pread(), but it automatically restarts pread()
+ * operations with a recoverable error (EAGAIN and EINTR). xpread() DOES
+ * NOT GUARANTEE that "len" bytes is read even if the data is available.
+ */
+ssize_t xpread(int fd, void *buf, size_t len, off_t offset)
+{
+       ssize_t nr;
+       if (len > MAX_IO_SIZE)
+               len = MAX_IO_SIZE;
+       while (1) {
+               nr = pread(fd, buf, len, offset);
+               if ((nr < 0) && (errno == EAGAIN || errno == EINTR))
+                       continue;
+               return nr;
+       }
+}
+
 ssize_t read_in_full(int fd, void *buf, size_t count)
 {
        char *p = buf;